GEORGIA STATE DIVISION OF CONSERVATION DEPARTMENT OF MINES, MINING AND GEOLOGY GARLAND PEYTON, Director THE GEOLOGICAL SURVEY Bulletin Number 51 SILLIMANITE AND MASSIVE KYANITE IN GEORGIA (A Preliminary Report) By A. S. FURCRON Assistant State Geologist and KEFTON H. TEAGUE Assistant Geologist Tennessee Valley Authority (With discussio,n of concentration by J. Bruce Clemmer, Carl Rampacek, and B. H. Clemmons, and refractory properties by T. N. McVay) Published in Cooperation .,.;ith the Tennessee Valley Authority ATLANTA 1 9 4 5 .......... L. ~ ,Ji. . "\ ..... ~ Residual boulders of massive kyanite, Pickens County. ~ LETTER OF TRANSMITTAL Department of Mines, Mining and Geology Atlanta, March 27, 1945 , His Excellency, Ellis Arnall, Governor Commissioner Ex-Officio, State Division of Conservation Sir: I have the honor to submit herewith Georgia Geological Survey Bulletin No. 51, "Sillimanite and Massive Kyanite in Georgia," by Dr. A. S. Furcron, Assistant State Geologist, and Refton H. Teague, Assistant Geologist of the Tennessee Valley kuthority. This bulletin has been prepared and published in cooperation with the Tennessee Valley Authority and the U. S. Bureau of Mines. The report announces the discovery in Georgia of two economically-important refractory minerals in commercial quantities, namely, sillimanite and massive kyanite. An extensive deposit of sillimanite was discovered in the course of the work in Hart, Elbert, and Madison counties, and deposits of massive kyanite previously known only from India were discovered in Cherokee, Pickens, and Dawson counties. Both of these minerals are regarded as essential ingredients in mixtures from which superduty refractory furnace linings and special electrical porcelains are manufactured. These deposits not only constitute our first discovery of domestic supplies of these raw materials in worthwhile quantities, but when considered in combination with Georgia's kaolins and bauxitic clays they are believed to constitute the basis of probable new manufacturing industries in Georgia. It is desired to point out the fact that this bulletin illustrates more nearly the ideal arrangement for conducting federalstate cooperative projects. In the first place, without the cooperation of the Commerce Department of the Tennessee Valley Authority, it would have been impracticable to consider launching the project. The Tennessee Valley Authority cooperated by making available a geologist to work with a geologist from this office in conducting the field work, and assisted in publication. The U. S. Bureau of Mines added materially to the practical commercial value of the bulletin by contributing chapters setting forth the results of their research on the beneficiation and utilization of both siPimanite and kyanite. Respectfully, GARLAND PEYTON Director. v CONTENTS ABSTRACT __________ ------------- ----- ------------------------------------------------ 1 FIELD WORK AND ACKNOWLEDGMENTS ___ -------------- 3 PART I Sillimanite PHYSICAL PRO PERTIES --------- - ----------- -- ------- ------------------ 6 USES OF SILLIMANITE ----------- -------------- ----------------------------- 6 OCCURRENCE OF SILLIMANITE______________________________________ 7 Sillimanite in Foreign Countries __________ ________________ ______ 7 Sillimanite in United States____________________________________________ 9 Sillimanite in Georgia ____ _ _ 9 CLASSIFICATION OF SILLIMANITE DEPOSITS IN GEORGIA __________________________ -------------- ___ ___ ___ _ ------------- 10 SILLIMANITE IN HART, ELBERT AND MADISON C0 UNTIES ________________________________ -------------- ________ ________________ 11 Location __________________________________________ --~-------- _________ _____ _______ 11 A ccessib ility ____________ -------------- _____ ____________________ ____ __________ 12 Topography, Streams, and Climate ____________________________ 12 Description of Sillimanite ____________ ----------------------------- 13 Geology of Deposits ------------------------------------------------------- 15 Size of Deposits---------------------------------------------------- _________ 16 Description of Deposits ----- _____________________ ____________________ 17 REFRACTORY PROPERTIES OF GEORGIA SILLIMANITE (Including Beneficiation)-------------------------------- _ 19 SILLIMANITE IN TOWNS COUNTY, GEORGIA, AND CLAY COUNTY, NORTH CAROLINA--------------------------- 23 Location of Deposits ___________________ ------------------------------ 23 Topography, Water Resources and Accessibility _______ 23 General Geology and Petrology____________________________________ 24 Description of Ore ______ --------------------------------------------- _ 25 Distribution of Deposits----------------------------------------__________ 26 Sampling and Concentration _________ --------------------------------- 28 Origin of Deposits ------------------------------------- _____ ________ ___ 28 PART H Massive Kyanite Deposits and Aseociated Rocks INTR0 D U GTI 0 N _________________ . ---------------------- ________________________ 30 TOPOGRAPHY AND DRAINAGE--------------------------------------- 30 VII C 0 NT EN T S (Continued) EARLIER PRE;-CAM::SRIAN ROCKS____________________________________ 31 AmicaI oI a Gneiss ---------------------------------------------------------~ 31 Distrib ution _______ ---------------------------~------------------------ 31 GeoIogy and PetroI ogy------------------------------------------ 31 LATER PRE-CAMBRIAN ROCKS--------------------------------------- 34 0 glethorpe Formation -------------------------------------------------- 35 Biotite Gneiss, Graywacke, and Quartzite West of Nelson -------------------------------------------------------------------- 37 Murphy MarbI e ----------------------------~--------------------------------- 37 Stratigraphic Position and Geologic Age_____________ 39 I GNE 0 US R 0 CKS ---------------------------------------------------------------- 43 SHEARED R 0 CKS ___________ ----------------------------------------------------- 44 Tate Shear Zone _____ ---------------------------------------------------- 44 Dawsonville Shear Zone______________________ ~------------------------- 4 7 KYANITE DEPOSITS ----------------------------~----------------------------- 48 Massive Kyanite in India------------------------------------------------ 48 Kyanite in the United States__________________________________________ 49 Kyanite in Georgia------------------------------------------------~------- 49 PHYSICAL PROPERTIES OF KYANITK----------------------~---- 50 USES OF MASSIVE KYANITE____________________________________________ 52 CLASSIFICATION OF KYANITE DEPOSITS IN GE 0 RGIA --------------------------------------------------------------------- 52 DESCRIPTION OF MASSIVE KYANITE DEPOSITS _______ 53 Size of Deposits ---------------------------------------------------~--------- 53 Distribution of De posits----------------------------~------------------- 53 Accessibility ------------------~----------------------------------------------- 55 Description of Ore __"---~------------------------------------------------c-- 55 Prospecting Kyanite ------------------------------------------------------ 56 o.rigin ------------------------------------------------------------------------------ 57 REFRACTORY PROPERTIES OF GEORGIA MASSIVE KYANITE ---------------------------------------------------------------------------- 58 Preliminary Firing of Small Lump Samples________________ 58 Preparation of Kyanite for Brick Tests _____________________ 62 Composition and Molding of the Test Brick________________ 66 Heat Treatments -----------------------"------------------------------~------ 66 The Variable High Temperature Load Test _______________ 67 ResuIts _______--------------------------------------------------------------------- 69 Discussion of Results ___________________________c------------------------ __ 71 VIII C 0 NT EN T S (Continued) Laboratory Work to be Done________________________________________ 72 Recommendations ---------------------------------------------------------- 74 REFERENCES __________ ------------------------------------------------------------- 75 MAPS Plate 1. Index map showing location of sillimanite and massive kyanite in Georgia-------------- __________________ 5 Plate 2. Plate 3. Sillimanite-bearing schist in Hart, Elbert and Madison co unties ---------------------~--------------------------- 10 Geologic map of the .southern end of the Blue Ridge Mountains in Georgia________________________________ 30 HGURES Frontispiece. Residual boulders of massive kyanite, Pickens County. Figure 1. Sillimanite crystals in biotite. gneiss, head- waters of Coldwater Creek about 6 miles southwest of Hartwell, Hart County________________ 14 Figure 2. Oglethorpe formation, on Burnt Mountain, Pickens County, containing typical ellipsoidal granite intrusions ---------------------------------------------- 32 Figure 3. New York quarry, Marble Hill, Georgia, viewed from the north. The marble dips to the south under Amicalola gneiss ------------------- 32 Figure 4. Hornblende gneiss stringers and lenses in marble, quarry on east bank of Long Swamp Figure Creek, 1 mile northeast of Tate Post Office, Pickens County ---------------------------------~----------------- 3 6 5. Contact between Murphy Marble (beneath) and biotite garnet gneiss (above), on road near Long Swamp Creek about 2Y4 miles southeast of Jasper, Pickens County _______________ 38 Figure 6. "Stretched pebbles" produced by shearing of a quartz vein, 1 mile north of Burroughs Cross Roads, Cherokee County__________________________________ 41 Figure 7. Pseudo-conglomerate composed of sillimanite- quartz lenses in Amicalola gneiss, 1 mile west of old Johnstown on State Highway 108, Daw- son County -------------------------------------- __________________ 41 Figure 8. Sheared quartz vein producing "stretched peb- bles" or pseudo-conglomerate, 1 mile north IX C 0 NT EN T S (Continued) of Burroughs Cross Roads, Cherokee County 45 Figure 9. Ribbon quartz produced by shearing of a quartz vein, 3 miles northeast of Ellijay, Gilmer County -------------------------------------------------- 45 Figure 10. Bou.lder of massive kyanite in place in mica schist, 2 miles east of Tate Post Office, Pickens County -------------------------------------------------- 51 Figure 11. Button-like lenses of massive kyanite in mica schist, 1% miles south of Holcomb, Pickens County, __ -------------------------------------------------------------- 51 Figure 12. Large residual boulder of massive kyanite, near headwaters of Yellow Creek, Dawson County :________________________________________ ____________________ _ 54 Figure 13. Figure 14. Residual boulders of massive kyanite, 2% miles east of Tate Post Office, Pickens County 54 Th~ maximum and minimum volume expansion and porosity changes of small fired massive kyanite h:rmps____________________________________________ 59 Figure 15. Top view of pile of Georgia massive kyanite lumps after heating to 1600 C.. in a round oil-fired kiln. Three slagged areas on side walls show position of silicon carbide brick ____ 61 Figure 16. One of the best lumps after firing, showing a minimum of staining. Two patches of quartz inclusions are seen at the left __________________________ 65 Figure 17. A large lump with about the average amount of slag or discolored spots. The expansion during heating has caused the typical splitting into one longitudinal crack with six cross splits and numerous small cracks ------------------ 68 Figure 18. Figure 19. The worst slagged lump in the second or 800pound shipment. The black slagged portion was about 1-inch deep-------------------------------------- 70 One-half of this lump split and fell off during firing leaving the white interior exposed. The top left portion has fallen away in a pyroplastic fashion from a position of alignment with the f'entral pinnacle__________________________________ 73 X ABSTRACT The report discusses deposits of sillimanite and massive kyanite in Georgia. Part one of the report describes sillimanite deposits recently discovered in Hart, Elbert, and Madison counties, Georgia, and from Towns County, Georgia, and Clay County, North Carolina. The report also covers the geology, classification, distribution, uses, and other economic features of the mineral. The sillimanite in the Georgia-North Carolina area was sampled by the writers, and concentrates were prepared by the Department of Chemical Engineering of the Tennessee Valley Authority. " Large samples from the deposits in Hart, Elbert, and Madison counties were referred to the Southern Experiment Station, Department of Interior, U. S. Bureau of Mines, where sillimanite concentrates were prepared; tests for refractory values were conducted at the Electrotechnical Laboratory of the Bureau of Mines at Norris, Tennessee. Preliminary concentration indicated that this sillimanite ore is amenable to flotation. Chemical and screen analysis of the Georgia and South. Carolina sillimanite indicate that the ore from the two states is very similar. Firing tests conducted by the Electrotechnical Laboratory showed that refractories made of sillimanite meet both the reheat specifications of the American Society for Testing Materials and those of the United States Navy for superduty refractories. In high temperature loadtests, sillimanite brick have an excellent load-carrying capacity at elevated. temperatures, and in the alumina-silica class are probably exceeded only by the electrocast corundummullite. The second part of the report deals with deposits of massive kyanite recently discovered by the writers in Cherokee, Pickens, Dawson, and Gilmer counties. This section of the report does not duplicate data published in previous Bulletin 21 *, of the Georgia Geological Survey. Massive kyanite deposits occur in a complex of earlier preCambrian rocks (Amicalola gneiss) which occur in a triangular-shaped area at the southern end of the Blue Ridge * References are at the end of the report. 1 2 GEORGIA GEOLOGICAL SURVEY south of 1\Ct. Oglethorpe. Unconformable over this complex is an extensive series of biotite gneisses, graywackes, quartzites, and graphitic rocks of later pre-Cambrian age. The basal , portion of this series (Oglethorpe formation) is well exposed northwest of Mt. Oglethorpe. Later facies of this series are mapped west of Nelson and Tate. Areas of marble (Murphy marble) of probable pre-Cambrian age are mapped and described. The pre-Cambrian formations of the area are profoundly affected by an overthrust which extends northeastward from the vicinity of Canton to a locality northeast of Dawsonville. The pre-Cambrian rocks north of this fault line are greatly sheared. At the southern end of the Blue Ridge, Amicalola gneiss and Oglethorpe formation are thrust westward. Along the west side of this overthrust there is an extensive area of sheared rock which includes many of the deposits of Murphy marble (Plate 3). Under the discussion of massive kyanite the report de-, scribes briefly the occurrence of ore similar to that now imported into this country from India. Deposits of kyanite are classified, and the size, distribution, origin, and geology of deposits of the massive type in this part of the State are discussed. Samples of the kyanite ore were sent to the Electro..: technical Laboratory, Norris, Tennessee, where brick samples were made and given the preliminary standard tests for refractories. In general, satisfactory "superduty" refractories were made from the Georgia massive kyanite samples. Mineral stains and inclusions in the massive kyanite cause from 10 to,33 per cent loss during calcination. This loss is more pronounced in the smaller lumps. A coarse, compact, and sturdy grog was obtained from the Georgia mineral, and this was similar to that furnished by the fibrous and coarse crystalline grades of "India" kyanite but not equal to the best "India" corundum-kyanite. Grog of the Georgia massive quality has never been obtained from other domestic kyanite by direct calcination of original lumps. A coarse grog is desirable for quality of ware, ease of manufacturing, and in the production of spall-resistant refractories. Standard size brick made from the Georgia kyanite were SILLIMANITE AND MASSIVE KYANITE 3 lighter in weight and higher in pore space than those made from the ."India" corundum-kyanite. The sample brick vvhan fired to 1600 C. met the A.S.T.M. reheat specifications for "superduty" fire brick, and it is possible that they can be made sufficiently volume-constant to meet the Navy specifications. The longer firing period in commercial kilns may permit a temperature lower than 1600 C. which was used in laboratory practice. The load resistance of the Georgia kyan ite sample brick at high temperature was very satisfactory. FTIELD WORK. AND ACKNOWLEDGMENTS This work presents results of a continuation of cooperative projects between the Georgia Department of Mines, Mining, and Geology and the Tennessee Valley Authority upon the investigations of strategic minerals in Georgia. About three months of field work was done by the writerz in mapping and collecting data for the report dur:ng 1944. The writers are preparing another paper upon the structure and stratigraphy of the Murphy marble belt in Georgia and North Carolina. The writers wish to express their appreciation for the encouragement and assistance of Captain Garland Peyton, Director, Georgia Department of Mines, Mining, and Geology, and of Mr. H. S. Rankin, Sanior Mining Engineer, Commerce Department, Tennessee Valley Authority. Mr. and Mrs. George W. Stose spent several days in the field with the writers where they reviewed the geologic map of the massive kyanite area, making valuable comment) and criticisms. The Department of Chemical Engineering of the Tennessee Valley Authority prepared numerous thin sections of the rocks of the region; also they prepared concentrates of sillimanite collected in the Davy Mountain area. Dr. James L. Calver and W. T. McDaniel, Jr., Geologists for the Tennessee Valley Authority, traced the Davy Mountain sillimanite belt in North Carolina to a point east of Hayesville. The maps used in the report were prepared by the Drafting Department of the Tennessee Valley Authority under the supervision of the writers. 4 GEORGIA GEOLOGICAL SURVEY The writers wish to acknowledge the assistance of members of the staff of the United States Department of the Interior, Bureau of Mines, at the Southern Experiment" Station, Tuscaloosa, Alabama, and the Electrotechnical Laboratory, Norris, Tennessee. A concentrate of the Hart County ore was prepared at the Southern Experiment Station, Will H. Coghill, supervising engineer, under the direction of Mr. J. Bruce Clemmer, Metallurgist, assisted by B. H. Clemmons and Carl Rampacek. The refractory values of the massive kyanite and sillimanite were determined at the Electrotechnical Laboratory under the supervision of Dr. Hewitt Wilson. Dr. T. N. McVay of the Southern Experiment Station and his assistants prepared the sections of the report which deal with the refractory values of the massive kyanite and sillimanite. Dr. M. V. Denny of the Mineralogical Laboratory of the University of Michigan checked the writers' identifications of sillimanite and kyanite by means of powder photographs. 6S" 83~ I INDEX MAP SHOWING LOCATION Of SILLIMANITE AND MASSIVE KYANITE IN GEORGIA PLATE 1 6 GEORGIA GEOLOGICAL SURVEY SIL.IJ~JLANITE PHYSICAL PROFERT!ES OF SILLIMANITE The following is a brief general description' of the mineral sillimanite. For a more complete discussion of the physical and chemical properties the reader is referred to the standard works on mineralogy. Sillimanite has the theoretical chemical composition A12Si05, and when heated above 1600" C. converts to a mixture of mullite (3A120a.2Si02) , and silica or siliceous glass. This mixture, has a specific gravity of about 3.15. Sillimanite has a hardness of 6 to 7, vitreous, silky to subadamantine luster, specific gravity of 3.2 to 3.3, and is gray to bluish-gray in color. Under the binocular, the crystals are transparent. The mineral may occur as dense, fibrous mats (fibrolite) composed of fibrous, sometimes radiating hair-like crystals in schist where it is associated with igneous intrusions. Examples of this type of material are some of the Davy Mountain deposits, and numerous small deposits scattered throughout the schists of North Georgia. Sillimanite also occur as bundles of crystals disseminated in biotite schist, as noted in the Hart-Elbert-Madison County .area. Sillimanite may often be confused in the field with the am- phiboles, especially tremolite, but these minerals may be separated on the basis of hardness and specific gravity, since sillimanite is considerably harder and is also heavier. The index of refraction of sillimanite is much greater than that of tremolite, silliman~te having an index of refraction of from 1.659 to 1.68, whereas tremolite has an index of re.i:raction of 1.602 to 1.650. In most sillimanite deposits more or less sericitization has taken place, but the presence of this type of alteration may be readily detected in the field by a test for l).ardness. USES OF SILLIMANITE For the past thirty years there has been a tendency in the ceramic and metallurgical industries towards the use of raw materials which can withstand higher te.mperatures in the SILLIMANITE AND MASSIVE KYANITE 7 manufacture of their products. At present a number of high grade alumina products are made from several sources including: the crystalline corundum produced in the electric furnace from bauxite, corundum-mullite electrocast refractories made from a mixture of bauxite and fireclay, mullite refractories made from domestic and "India" kyanite, and small amounts made from western domestic andalusite, as well as a little made from South Carolina topaz. One of the best qualified minerals for high temperature refractories is sillimanite. The mineral has an advantageous characteristic over "India" kyanite and topaz in that it does not require pre-calcining before incorporation into a body for service, at least, below 1600 C. Although sillimanite deposits are known in Australia, India, and Africa, industry has not yet accepted it as an ore. Domestic sillimanite ores must be concentrated, also it will be necessary to remove iron stains before the concentrates can be used in the highest grade refractories; however, few serious attempts to beneficiate the ore have been made~ Some of the more prominent potential uses for sillimanite are: porcelain for spark plugs, high grade refractory bricks, crucibles, saggers of all types, boiler linings, high temperature cements, linings for indirect-arc and heat treating furnaces, pyrometer tubes, glass tank blocks, et cetera. OCCURRENCE OF SILLIMANITE Sillimanite in Foreign Countries Sillimanite has been observed from many localities in the world, but most of the deposits discovered thus far have been small and non-commercial. The mineral is not infrequently encountered as small radiating prisms in metamorphic rocks, especially schists. In the field it is easily overlooked, thus it may be more abundant than is generally thought. Rather large deposits of the mineral have been reported from Mongmaweit Village at Khasi Hills, Assam, and from Pipra, Rewa, India. A minimum reserve of 182,600 tons is estimated for these two localities. 4 The Assam deposits are very inaccessible. The deposits generally consist of massive 8 GEORGIA GEOLOGICAL SURVEY sillimanite with a little corundum in highly aluminous rocks .such as sillimanite-quartz s~hists interbedded with cordieritebiotite-quartz microcline gneiss. Thirteen different deposits occurring over a belt 3 miles long and a mile wide were discovered by Dunn during the field season of 1927.rs The Pipra deposits occur in pre-Cambrian rocks in Rewa State, Central India, where in 1927 the ore was transported by ox cart 120 miles to Mirzapur. Most of the rock consists of sillimanite schist containing local segregations of corundum- sillimanite. Sillimanite has been reported by Simpson22 from the north- western shore of Weelhamby Lake in Ninghanboun Hills of Western Australia. The rock is coarsely granular quartz with dense bundles of sillimanite fibers. Sericite, muscovite, biotite, garnet, feldspar, chlorite, and some andalusite are asso- ciated minerals. In another locality near by, sillimanite occurs in granular quartzite. Long narrow lenses of andalusitemuscovite schist are interbedded with the sediments associated with the sillimanite, and large angular pebbles of pure crystalline andalusite up to 50 pounds in weight occur which were derived from highly quartzose pegmatites which cut hornblende schist. Other sillimanite deposits from western Australia have been described, and commercial deposits are known from the vicinity of Clackline 23 where it occurs in a primary clay which lias been used for over 30 years in the manufacture of firebricks. It is found in seams as thin plates and small lenticular "eyes" of almost pure sillimanite, which mineral constitutes about 5 per cent of the entire mass. Simpson concludes from his observations, "that the greater part of clay used in the making of firebricks at Clackline is a highly kaolinized biotite schist of the Chittering pre-Cambrian series. Originally this rock was probably highly glauconitic shale."2s The Board of Economic Warfare recently investigated a sillimanite deposit from the Broken Hill District, New South Wales. Sharpstone states*: "By way of explanation may we state that at no time have we been especially interested in the sillimanite deposit in question since, when we ~id have a pur- * Sharpstone, David C., personal communication, April 25, 1944 SILLIMANITE AND MASSIVE KYANITE chase directive, it specifically called for Indian kyanite. Furthermore, shipments from Australia received by Philipp Brothers, Incorporated, 70 Pine Street, New York, and by Chas. Taylor Sons, Cincinnati, proved that the material could not be considered a substitute for Indian kyanite. To my knowledge Philipp Brothers received a shipment of 60 tons, and they report that it turned out useless; Charles Taylor Sons received a two-hundred ton shipment, and they state that it is not practical to adapt it to the uses of Indian kyanite.'' Sillimanite in the United States In the United States, small unimportant deposits have been reported from several counties in California, from Massachusetts, Connecticut, New York, Pennsylvania, Delaware, Virginia, North Carolina, etc.; a few tons of sillimanite are reported to have been produced from North Dakota. Forrester5 has described a sillimanite deposit near Troy, Latah County, Idaho. A report on sillimanite deposits in the Monadnock Quadrangle, New Hampshire, by Mrs. Billings2 has been published :recently. The deposits appear to be small, but descriptions of them in the report indicate that they resemble the ones in Hart, Elbert, and Madison counties, Georgia. About a year ago members of the Soils Survey of the U. S. Department of Agriculture discovered sillimanite in the schist in Spartanburg and Greenville counties, South Carolina. Smith24 in 1943 briefly described these occurrences in the Engineering and Mining Journal. Recently, W. H. Hudson11, of the U. S. Bureau of Mines, Gainesville, Georgia office, has sampled and studied several of the deposits. The South Carolina deposits resemble the ones; described in this report from Hart, Elbert, and Madison counties, Georgia. SilHmanite in Georgia In the summer of 1943 Dr. R. J. Smith submitted a sample of sillimanite from Davy Mountain, North Carolina, on the Georgia State line, to the Georgia Department of Mines, Mining and Geology. The sample was discovered by Ab Ford of Warne, North Carolina, who pointed out the location of the deposit to Furcron. A joint project between the Georgia De- 10 GEORGIA GEOLOGICAL SURVEY partment of Mines, Mining and Geology and the Mineral Section of the Regional Products Research Division of Tennessee Valley Authority was organized, and Furcron and Teague traced this zone into Georgia to the vicinity of Hunter Knob, Towns County. Dr. James L. Calver and W. T. McDaniel, Jr., Geologists for the Tennessee Valley Authority traced the belt northeastward into North Carolina to the vicinity of Tusquitee. Several of th.ese localities were prospected; samples were collected and a sillimanite concentrate was prepared from the samples ~Y the Chemical Engineering Department of the Tennessee Valley Authority. In September, 1944 the extensive area of schists and gneisses east of Atlanta designated as "Carolina gneiss" on the State Geological map _9 were investigated by Furcron and Teague. Small local occurrences of sillimanite are quite common in the area, but a belt of schist rich in sillimanite was discovered and described from Hart, Elbert, and Madison counties. Several of the better localities from this belt were prospected by the writers, and the samples were sent to the U. S. Bureau of Mines where a sillimanite concentrate was prepared at the Southern Experiment Station, Tuscaloosa, Alabama. CLASSIFICATION OF SILLIMANITE DEPOSITS IN .GEORGIA Several types of sillimanite deposits have been noted during the course of this study. The deposits exhibit parallel features in classification with kyanite. (1) Sillimanite crystals and bundles of crystals disseminated in schist which have been intruded and recrystallized by granite and pegmatite. This type of deposit seems to offer most promise for the commercial production of sillimanite. Deposits in South Carolina, the belt described in this report ' from Hart, Elbert, and Madison counties, Georgia, and the de,. ,~ posits near Mt. Monadnock, New Hampshire, belong in this .tU,; class. (2) . Stringers and lenses of fibrolite, or fibrous sillimanite and quartz in schist associated with. intrusive pegmatite and granite; the stringers may or may not be crosscutting; also they may be sufficiently' abundant to form zones of sillimanite schist which generally parallel pegmatite intrusions. GEORGIA GEOLOGICAL- SURVEY BOWERSVILLE I I i 1/1 ~- " . I I I . I I ROYSTON PLATE 2 PLATE 2 D.S.O. VLH 102144 -, Scale 2 0 Z Miles tl~E3~~E3~~1======~I SILLIMANITE BEARING SCHIST IN HART, ELBERT, AND MADISON COUNTIES 6ranite and Included .sfr/nqers of m/ca sch/sf. TE NNSSEE VALLEY AU'THORI'TV Si/1/manlle- hearing_ .schl.:sf /nfruded ,.-,.-!. 1---&-u-e..--, o----:"CT-OP.-i:o-!!~cMo,-lMR-:-C.,I.-!:.-1!:D.,.I,!-:NcP,.A...R.T-P;M__-&-r.-N--AT=-::P~P~II.O:::-:-Y-:-E::-D~--t hy granite j oyerprlnf repre8en l.s zone of major concenfrof/on of sil!lmanife. KNOXVILLE 821BIOO:Ro SILLIMANITE AND MASSIVE KYANITE 11 The deposits described from the Davy Mountain-Brasstown Church area, and from many other isolated occurrences are of this type. These deposits are generally small; fine grinding is necessary in order to obtain a concentrate. (3) Nodules and segregations of massive sillimanite in schist; local occurrences noted from Davy Mountain and Hart County. (4) Button and flattened "pebble-like" masses of sillimanite (fibrolite) and quartz in schist. This peculiar type, "pseudo-conglomeratic" in character, is described from the region of Amicalola River in the second part of this report. (5) Sillimanite replacing kyanite. Examples of this type may be found in the Davy Mountain-Brasstown Church belt. Prindle 21 figures an occurrence of this type from Hyatt Mill Creek, 3 miles south of Hayesville, North Carolina. . SILLIMANITE IN HART, ELBERT, AND MADISON COUNTIES Numerous occurrences of sillimanite of the stringer or vein type and of the disseminated type are found in these counties. These deposits resemble those found in South Carolina; some of them appear to be better than the ones thus far described from that state. A zone of sillimanite schist of probable commercial value is described from these counties (Plates 1 and 2). Location Most of the deposits discovered recently in these counties occur in a belt of schist extending south and southwest of Hartwell (Plate 2). The belt has been traced for a distance of about 23 miles, extending from Hartwell southwe~tward through Hart County, through Elbert County, just east and south of Bowman, and through the eastern end of Madison County between Comer and Carlton to the Oglethorpe County line. The exact boundaries of the belt are obscured by weathering; its width is variable. Between Hartwell and Bowman the belt is approximately two miles wide, and the sillimanitebearing schist zone near its southwestern terminus is about a mile wide. This belt, illustrated in Plate 2, contains numerous zones of granite which are difficult to separate from the schist because rock outcrops are scarce and the soil covering is deep. The richest zone (Plate 2) is found near the middle of 12 GEORGIA GEOLOGICAL SURVEY the belt between Little Coldwater Creek, south of Hartwell and Holly Creek just southwest of the Elbert-Madison County line. Isolated occurrences of sillimanite-bearing schist have been found beyond the border of this belt, and detailed p~os pecting in the future may discover other belts with a high sillimanite content in this same general area. Accessibility The Seaboard Airline Railway crosses the southern end of the belt between Comer and Carlton, and a branch of the Southern Railway crosses the middle portion of the belt between Bowman and Elberton. This branch crosses the best part of the belt near Harper; it connects with the main line of the Southern at Toccoa and with the main line of the Seaboard at Elberton. Hartwell, at the northern terminus of the belt, is connected with the Southern Railway by the Hartwell Branch. Thus the best deposits are close to or only a few miles from rail transportation. The belt is also completely accessible to truck and automobile by paved highways and a net-work of secondary roads. State Highway Number 36 crosses the southern end of the belt between Comer and Carlton. Georgia Highway Number 17, another paved highway, parallels the Southern Railroad be- . tween Bowman and Elberton, connecting with U. S. Number 29 at Royston. A graded soil road parallels the eastern side of the belt between Elberton and Hartwell. Short stretches of secondary roads render all sections of the belt readily accessible to railways and improved roads. The large amount of quartz" from weathered granite imparts a sandy character to most of the soil roads so that they are passable generally at all times. Topography, Streams, and Climate The area under discussion lies in the eastern part of the Central Upland in Georgia. Most of the belt is in the northern part of the Washington Plateau which slopes from about 800 feet above sea level near Hartwell to about 500 feet at the southern junction with the Coastal Plain. The upland surface is flat, and slopes to the streams are gentle. SILLIMANI:"' Q l'l 0 t"" 0 "0 ' r)> en ~ " < t'l >( ~ I'XJ Figure 5. Contact between Murphy marble (beneath) and biotite garnet gneiss (above), on road near Long Swamp Creek about 2 % miles southeast of Jasper, Pickens County. SILLIMANITE AND MASSIVE KYANITE 39 bined carbonates generally range between 60 and 95 per cent. The white, fine-grained varieties are dolomitic with a MgO content as high as 20 per cent. The best marble of the belt thus far discovered for building and monumental purposes, occurs east of Tate near Long Swamp Creek. In this area the marble is massive and large blocks of marble free of joints and cleavage planes, and uniform in composition are obtained. An examination of the geological map (Plate 3) indicates that the hornblende gneiss is closely associated with the marble. Field evidence supports the view that the hornblende and actinolite associated with marble are derived from a calcareous facies of the formation, although all of these rocks have been mapped previously as of igneous origin. Brown biotite and calcite characteristic of the marble also occur in this hornblende schist. Bands and lenses of hornblende and hornblende and biotite occur locally in the marble, and hornblende schist and marble are interlayered opposite the Cherokee quarry. Other bodies of hornblende rock in the old gneisses are generally regarded as of igneous origin since those bodies contain an appreciable amount of garnet and feldspar. Stratigraphic Position and Geologic Age The term "Murphy Marble" is retained in this report although it would have been better if the formation had been named from the vicinity of Tate or Marble Hill where practically all of the commercial dimension stone is obtained, and where the ,deposits are best developed. The writers disagree with Keith's interpretation of the stratigraphic position and geologic age of the marble.l-4 Keith recognized in the Murphy marble belt above the pre-Cambrian gneisses a series of formations of Lower Cambrian age, the youngest of which are the Murphy marble and Nottely quartzite. The formation beneath the Murphy marble, he called the Valleytown. This rock type from Canton, Georgia to the Little Tennessee River in North Carolina consists of sheared rocks and green phyllites of dubious origin. Various writers have found it necessary from place to place to include almost every rock type of the area in the Valleytown formation in order to follow the original stratigraphic sequence of Keith. For these and other reasons given later there may be no Valleytown formation as described. 40 GEORGIA GEOLOGICAL SURVEY Reasons for assuming a Cambrian age for rocks of the Murphy marble belt have not been expressed clearly by Keith14, LaForge 16, and Bayley1 These rocks are not connected with Paleozoic sediments of established age, and no fossils have been found in them. The problem is further complicated by the occurrence of the marble with sheared rocks associated with established overthrusting. In the Marble Hill area the marble underlies the Amicalola gneiss. However, this gneiss is thrust over the marble at this locality. About one-half mile northeast of Tate Post Office on the road to Federal School, Amicalola gneiss over the marble is sheared. On the north side of the valley at Marble Hill immediately opposite the New York quarry, Amicalola gneiss containing sheared kyanite buttons appears to dip directly under the marble. A body of marble surrounded by hornblende gneiss is enclosed in Amicalola gneiss at the old Amicalola quarry about one mile south of Marble Hill. The marble body is intruded by miCa pegmatites. Two other similar occurrences of marble are found two miles north of Ball Ground. The writers have not found any physical indications of thrusting associated with these latter occurrences, thus the marble either occurs in the Amicalola gneiss or in some manner reached its present position through flowage. Elsewhere throughout the area of the geologic map (Plate 3) marble occurs generally with sheared pre-Cambrian rocks. At Whitestone, on the Gilmer-PiCkens County line, a block of slightly graphitic late pre-Cambrian quartzite and slate is thrust over the eastern side of the marble. The rocks beneath the marble are poorly exposed, but where observed they are sheared. In the old marble quarry at Marble, North Carolina the marble seems to have an anticlinal structure, and its northwestern limb dips northwestward under late pre-Cambrian graywackes which are garnetiferous, contain unaltered biotite porphryoblasts, and exhibit a double cleavage. One of the best exposures of marble is at Hewitts, Macon GEORGIA GEOLOGICAL SURVEY BULLETIN 51 FIGURES 6 AND 7 17~11\r.\ .(}A :'._o..t.no.\ :...--. Pough. Figure 6. "Stretched pebbles" produced by shearing of a quartz vein, 1 mile north of Burroughs Cross Roads, Cherokee County. Figure 7. Pseudo-conglomerate composed of sillimanitequartz lenses in Amicalola gneiss, 1 mile west of Old Johnstown on State Highway 108, Dawson County. 41 42 GEORGIA GEOLOGICAL SURVEY County, North Carolina, near the northern end of the belt. At this place all of the rocks dip southeast. Marble is exposed at the bottom and on both sides of the gorge of Nantahala River which at this place is over a thousand feet deep. The marble bed is completely enclosed by late pre-Cambrian rocks. On the east side of the gorge marble is well exposed along the highway where it dips under quartzite, graywacke, and biotitemuscovite-quartz slate which is. slightly graphitic. On the west side of the valley at the quarry it is underlain by green slaty phyllite which may be sheared. Below the phyllite and to the west are extensive deposits of late pre:-Cambriari quartzites .and slates. Most geologists will agree that the marble and immediate-enclosing rocks at this locality have been affected by thrust faulting, but even if faulting is present both above and below the marble it is difficult to explain its present position unless it is assumed that the marble occurs in this late pre-Cambrian series. The observations given above suggest that the marble is closely associated with Amicalola gneiss near the southern end of the Blue Ridge, but in the middle and northern portions of the belt it is associated with rocks classified as of later pre-Cambrian age. At present it is possible. fo suggest a number of hypotheses concerning its age and stratigraphic position, but the burden of evidence indicates that it is preCambrian. Much more detailed work should be done in this area, for not only are the relations of marble to gneisses obscure, but the origin of the green ph~llites is open to question; also the relation of Nottely quartzite to marble is not established. For these reasons the stratigraphic position of the Murphy marble as expressed in the legend (Plate 3) is regarded as tentative. The marble is an intensely metamorphosed rock-certainly much more highly altered than Lower Cambrian limestones and dolomites in the Great Valley. Crystals and bands. of biotite are numerous in it; tremolite is a characteristic mineral, occurring as individual crystals or as masses of tremolite and marble. Locally, the marble has been altered to hornblende and actinolite. SILLIMANITE AND MASSIVE KYANITE 43 IGNEOUS ROCKS Detailed descriptions of these rocks may be found in other reportsl. s. 1a, 29, A very brief description of the igneous rocks in the area studied is given belo\w. Hornblende Gneiss. Hornblende gneisses and amphibolites occur locally throughout the area. They are found in the Amicalola gneiss along Georgia Highway No. 53 east of the Dawson-Pickens county line. Elsewhere in the area of Amicalola gneiss they are found where they may be associated with pink granite. These rocks are especially prevalent in the vicinity of the marble in the Marble Hill area where some of the hornblende appears to have been derived from marble. Sheared hornblende gneisses are common in the Dawsonville shear. z.one where they are associated with the gold deposits. Occasional bodies of hornblende gneiss are found in the later pre-Cambrian sediments. These rocks are regarded as of pre-Cambrian age. Corbin Granite~ Small areas of this granite occur in the vicinity of Salem Church in Pickens County. Most of the rock is sheared and locally reduced to a sericite mylonite. The term "Salem Church granite" of Bayley1 is not retained here lilecause the granite is similar in all respects to the Corbin granite described by Hayes east of the Cartersville overthrust. This rock is a blue quartz, microcline granite which contains practically no mica. It is similar to certain other pre-Cambrian granites which are found in the Blue Ridge to the north. 7 Mica Pegmatites. A considerable amount of sheet mica has been produced from the Amicalola gneiss area south of Marble Hill. Another mica mining area is found in late pre-Cambrian graywacke and quartzite west of Nelson. These pegmatites are believed to be of late Paleozoic age. They are not found except in a highly sheared condition in the principal shear zones of the area. The location of the more important mines and prospects may be found upon the geologic map (Plate 3). A complete discussion of these and other micabearing pegmatites in the State has been published by the writers. a Diabase Dikes. Intrusive dikes of coarse to fine grained dia- 44 GEORGIA GEOLOGICAL SURVEY base are found in the crystalline rocks of the eastern part of North America from Nova Scotia to Alabama. These rocks are f:resh and undeformed, and correspond mineralogically to known intrusions of Triassic trapp in Nova Scotia, New York, New Jersey, Virginia, etc. The principal minerals of the diabase are usually augite and labradorite, but some of the dikes contain olivine. Bayley1 has described several dikes from this area. At the A. W. Amphlett mica mine, five miles east of Ball Ground, a diabase dike cuts the mica pegmatite. SHEARED ROCKS In this area several extensive zones of sheared rocks occur. These shear zones involve practically all of the rock types previous.ly described in this report. In many localities the rocks have been so deformed tha:t the original formation can- not be recognized because a secondary platy cleavage has completely obliterated the original structure. Where these processes are most intense, the rocks approach in physical character the appearance of mylonites. Certain retrogressive mineral changes may take place inthe rock. In this area feld~ spar alters to sericite, hornblende .and biotite to chlorite, and tremolite to talc. All stages between unaltered granites, gneis~ ses, and graywackes to completely sheared-out rocks may be observed. ' An extensive zone of deformed rocks here referred to as the Dawsonville shear zone lies north of an overthrust which extends from Canton northeastward through Dawsonville. West of the Marble Hill overthrust there is another extensive shear zone which follows the Murphy marble belt and unites with the Dawsonville belt in the vicinity of Canton. West of this belt other sheared rocks are present as indicated upon the geologic map (Plate 3). In the unsheared gneisses and -schist, dips are frequently gentle or rolling and strikes are variable, whereas in the shear zones, dips are uniformly to the east and southeast, and strikes are more regular. Thus a Sll;d- den change to a uniform southeastern dip is characteristic- of the sheared rocks. Tate Shear Zone This belt includes rocks previously mapped by Keith14, La- GEORGI A GEOLOGICAL SURVEY BULLETIN 5] F IGURES 8 AND 9 Figure 8. Sheared quartz vein producing "stretched pebbles" or pseudo-conglomerate, 1 mile north of Burroughs Cross Roads, Cherokee County. Figure 9. Ribbon quartz produced by shearing of a quartz vein, 3 miles northeast of Ellijay, Gilmer County. 45 GEORGIA GEOLOGICAL SURVEY Forge16, and Bayley1 as belonging to the Nantahala, Valleytown, and Murphy marble formations of Lower Cambrian age. However, the various facies of the sheared rocks appear to represent sheared equivalents of various types of pre-Cambrian rocks. Most of the previous writers have identified extensive effects of shearing, but seem not to have attached sufficient significance to the observation. Bayley1 (page 67) notes that the Valleytown formation of the Tate quadrangle consists mainly of graywacke beds and thinly layered silverly garnetiferous mica schist. He calls special attention to the amount of shearing in the rocks., stating "where very greatly sheared, the Valleytown mica schists are thin plates of crowded mica flakes that readily break down and furnl.sh a soil that consists almost exclusively of mica flakes and a few garnets." The Tate shear zone is about six miles in width at its junction with the Dawsonville shear zone near Canton. The belt becomes narrower to the north and varies considerably in width of outcrop. For example, at Ellijay the belt is less than one mile wide. It is not easy to understand if these rocks were normal formations how, with their great thickness in the vicinity of Canton and Ball Ground, they could all pass through such a narrow s.pace at Ellijay. In a region where all the massive rocks are in.ltruded by granites and late Paleozoic pegmatite, the absence of intrusions in these zones is striking and significant. The writers believe that the igneous intrusions in the shear zones have been completely sheared out so that their identity has been destroyed. Two miles southeast of J.asper, and about one-half of a mile west of the marble quarry on the road to Long Swamp Creek Church, a sheared mica pegmatite is exposed in the road. The feldspar is altered to sericite, and the quartz is shea:red into thin plates and rolled parallel to the schistosity. The small mica books have been rounded and also oriented. Granites have been extensively sheared in the area around Salem Church in Pickens. County. All stages from unaltered granite to a mylonite consisting entirely of sericite, with more or less quartz, occur; the pure apple-green laye:rs of sericitemylonite have been mined for years in this district. Hornblende gneisses are altered to chlorite schists. These rocks SILLIMANITE AND MASSIVE KYANITE 47 resemble basic rocks in the northwest Highlands of Scotland where they are sheared into chlorite schists on the soles of thrust blocks. Sheared-out chloritized rocks of this type are abundant, and well exposed where they are mined north of Capton. Although recrystallization prevails over simple cataclastic structure in the less resistant rocks, massive quartzose and arkose beds, and quartz veins, tend to be sheared out without much chemical alteration, at least toward the western and northwestern side of the shear zones whre the non-resistant rocks have lost their original structure. Where the effects of differential movement have become less, extensive granulation and cataclastic structures are developed in the resistant rocks. The feldspars and quartz in the arkose beds are smeared out into long knotty strings. The most peculiar effects are noted in the quartz veins and occasionally in conglomerates. Where the veins are thin, the quartz is smeared out into long parallel ribbons. In many places, the veins have been sheared out into elongated pebble-like fragments described by McCallie as "stretched pebbles." These pseudo-conglomerates have not been noted in the intensely sheared rocks. They may be encountered along the roads wherever quartz veins were pres.ent before thrusting took place, to form a sort of zone between the sheared and unsheared rocks. Examples of such sheared-out quartz veins or pseudo-conglomerates may be seen on the road between the paved highway and Whitestone, on a dirt road just west of the paved highway 2.5 miles north of Ellijay, and along the roads one and onehalf miles north of Burroughs Crossroads some eight miles north of Canton. Effects somewhat similar to this have been observed in sheared out granite in the vicinity of Salem Church where large quartz grains are involved. Dawsonville Shear Zone This belt has an average width of four or five miles in the region under discuss.ion. East, south and southwest of Dawsonville, extensive granite intrusions appear in the overthrust block southeast of the shear zone. The rocks of this belt consist of the sheared equivalents of granite, graywacke, biotite schist, and hornblende gneiss now in the form of thinly pli- 48 GEORGIA GEOLOGICAL SURVEY cated chlorite schist, muscovite-chlorite-quartz schist, etc. Many of the beds are garnetiferous. One facies described by Bayley1 as "Canton schist" is a glistening, bluish gray, garnetiferous mica schist which contains a small amount of graphite. Chlorite schist derived from hornblende gneisses are especially well exposed south and southwest of Dahlon~ ega. Quartz veins and stringers which post~date thrusting are common in this sheared belt. In fact, the prominent g:old mines are located in this zone of sheared rocks. Near the western or northwestern side of the belt, quartz veins that preceded thrusting are sheared into pseudo-conglome:r:ates which may be observed along the dirt roads south and southwest of Keithsburg. They have been produced also in the Amicalola gneiss by local shearing about two miles south- of Ball Ground. KYANITE DEPOSITS The mineral kyanite is widespread in areas of crystalline rocks although the massive form described in this report has been recognized previously only from India. Massive Kyanite in India Kyanite rock from Lapsa Buru, India, was shipped before the war from Calcutta to England, the United States, Ger~ many, Belgium, and Italy. Kyanite production began in India in 1924, and had totalled 33,000 tons by the end of 1933. Production has increased since that date so that 24,886 tons were exported from India in 1937. Over 96 per cent of the kyanite came from Lapsa Hilla in Kharsawan, where it was quarried by the India Copper Corporation, Ltd. Shipments of India kyanite have been curtailed recently partly by lack of shipping facilities and partly by threat of Japanese in~ vasion. Although 14,285 short tons valued at $175,218 were imported from India in 1941, our imports dropped to 6,524 tons with a value of $93,743 in 1942. During 1941, the shipping rate on kyanite imported from Calcutta increased from $11.20 to $16.80 a short ton, and the price rose from $25.00 to over $30.00 a short ton. In 1942 the price of India kyanite was $54.00 a short ton. At Lapsa Hilla segregations of massive kyanite occur in SILLIMANITE AND MASSIVE KYANITE 49 beds of kyanite-qua.rtz rock which is associated with muscovite and hornblende schists. Corundum is a common mineral in the massive kyanite segregations. Dunn believes that these deposits are the metamorphic products of highly aluminous or bauxitic clays. He estimates a minimum of 234,000 tons of massive kyanite in the Lapsa Buru deposit at the western end of the belt, and about 38,000 tons for other deposits. Kyanite in the United States Extensive deposits of kyanite occur in the eastern part of -the United States in the crystalline mica schists. These deposits consist of crystals. of kyanite disseminated in mica schists and quartzites. They are mined extensively in Virginia at Baker Mountain in Prince Edward County, and by the Celo Mines Incorporated (now Mas-Celo Mines Incorporated) at -Burnsville, North Carolina. At present the latter operation is inactive. Kyanite from the belt in South Carolina, Georgia, and Alabama is not mined at the present time. Kyanite in Georgia The most important mined deposits of kyanite in Georgia are found in a "U"-shaped belt which is about 30 miles long and from 100 feet to a quarter of a mile wide in Habersham and Rabun counties north of Clarkesville. 21 2 5 This type of Qre has been extensively worked by Philip S. Hoyt of the Southern Mining and Milling Company, Clarkesville, Georgia, and by the A. P. Green Fire Brick Company of Mexico, Missouri. Flat crystals of kyanite up to 1;2 inch in width are disseminated through the mica schist which also contains small amounts of graphite. Similar occurrences have been described in the Ellijay folio 1 6 and are common from other parts Qf the State. The amount of kyanite in the schist ranges from 1 to 15 per cent, with a general average of 6 to 8 per cent at places available for mining. Locally in the belt, kyanite crystals are abundant in the soils overlying the schist. Placer deposits have been worked near Clarkesville. Veins and lenses of coarsely-bladed kyanite occur in mica schist, and locally are associated with quartz lenses. Deposits of this type are usually small veins, or smaller lenses and nodules that are quite resistant to weathering; thus dornicks 50 GEORGIA GEOLOGICAL SURVEY and boulders of kyanite from such occurrences may be found locally in the break-down over the primary schist and gneiss. Very little kyanite of this type has been mined in the State~ probably because the deposits are small and lack continuity. A kyanite deposit on Gumlog Mountain in Towns County was prospected in 1931 by the A. C. Spark Plug Company. Very little ore was shipped. At Graves Mountain in Lincoln County, crystals and aggre- gates of kyanite replace quartzite. The types of kyanite mentioned above have been discussed in P:rindle's21 report by D. W. Johnson. In Decemb~r 1939, Mr. .T. M. York submitted several speci~ mens of massive ky.anite from the property of A. J. Elkins of Dawson County to the Georgia Geological Survey. The writers later examined this property and discovered numerous occurrences of similar material in Dawson, Pickens, Cherokee, and Gilmer counties. As far as is known, this is the only occurrence of this massive type of kyanite discovered thuS' far outside of India. PHYSKAL PROPERTIES OF KYANITE Some of the more commonly used physical properties of kyanite are given below. Kyanite, like sillimanite, has the chemical composition of A12Si0"; when heated above 1350 C. it is converted to a mixture of mullite and silica or silica glass. The variety of kyanite found disseminated in schists, and also the type of interlockingtabular blue-bladed crystals associated with quartz veins and pegmatites, have a unique, hardness. The hardness parallel to the long direction of the blades is 4, whereas across the crystals it is 7. These varieties .are blue to bluish-gray in color, generally with the deepest color arranged in streaks or bands. Specific gravity of the mineral varies from 3.5 to 3.7; luster is vitreous to pearly. The massive kyanite described in this report is unique in that the individual crystals seldom exceed an eighth of an inch in length. Also the crystals are tightly interlocked to form dense, compact masses with little or no pore space. The varieties of kyahite described in the above paragraph, when calcined beco:rpe friable, whereas the massive variety remains GEORGIA GEOLOGICAL SURVEY BULLETIN 51 FIGURES 10 AND 11 Figure 10. Boulder of massive kyanite in place in mica schist, 2 miles east of Tate Post Office, Pickens, County. Figure 11. Button-like lenses of massive kyanite in mica schist, 1 1fz miles south of Holcomb, Pickens County. 51 52 GEORGIA GEOLOGICAL SURVEY dense and tough. The field test for hardness on massive kyanite is of little value. Boulders of massive kyanite are bluish gray to grayish white in color; they may be confused in the field with massive barite~ but are much tougher and more difficult to break than barite; also massive kyanite frequently contains corundum. The index of refraction of kyanite is from 1.712 to 1.728, thus distinguishing it from sillimanite with refractive indices of 1.659 to 1.680. USES OF MASSIVE KYANITE Massive kyanite from Georgia may be used in the same general type of refractories. as the kyanite now imported from India. Refractories which use kyanite as the principal constituent are classified as high alumina refractories (approxiirfately 60 per cent A120a). Refractories made from calcined massive kyanite have a low coefficient of expansion under service conditions, comparatively high melting peints, and resistance to loads at high temperatures, thermal shock, corrosive action of certain fluxing agencies, and furnace gases. McVay and Wilson17 give the more important uses of massive kyanite as "(1) linings for Ajax-Wyatt induction and indirect arc furnaces for melting and refining brass and bronze containing more than 75 per cent of copper and those metals that require higher temperatures than does yellow brass, (2) furnaces in which silica brick can be used for continuous service but spall during intermittent operation, (3) oil-burner ports and blocks, (4) super-structure for glass tanks exclusive of the silica-brick crowns, including the forehearth and mechanical feeder parts for forming machines and (5) heavily loaded kiln furniture for fast schedules in ceramic firing." CLASSIFICA,TION OF KYANITE DEPOSITS IN GEORGIA Several types of kyanite deposits. have been noted duringthe course of this study. Although kyanite seems to be formed at a lower temperature than sillimanite, the two minerals show marked similarity in origin and m