Document 99v5mn22dYRODxYEe8ogyKE13

FILE NAME: Talc (TALC) DATE: 1998 DOC#: TALC110 DOCUMENT DESCRIPTION: Book Excerpt - Mineralogy Textbook Talc 1 ' M ' : \ T H NEW YORK : u PUBLIC LIBRARY fi) , - '-1' A S T O n , L F N O X A I J K , A TEXT-BOOK OF M I N E B A L O G -Y WITH AN EXTENDED TREATISE ON CBYSTALLOGRAPHY AND PHYSICAL MINERALOGY BY EDWARD SALISBURY DANA N E W EDITION, ENTIRELY REWRITTEN AND ENLARGED WitJj nrarIs 1000 bigarra ant a (tolorrt JHatr NEW YORK JOHN WILEY & SONS L ondon : CHAPMAN & HALL, Lim ited a * r THE NEW YORK PUBLIC LIBRARY 5811378 A8TOH, LENOX AND TILD EN FOUNDATIONS. R 19,3 l Copyright, 1888, by tow ard s. daka: .. . ftrUtOHk 9m *otw rl Braaumiad tii flSojnpmm Rmf mk 8ILICATES. 479 DeweyUte. A mncneaian silicate near serpentine but with more water. Formula perliupa 4MgO 3k>iOs.6HiO. Amorphous, resembling gum an&bic, or a resiu. H, = 2 ? 5' . 2 72 ? wbillslj>yellowish, reddish, brownish. Occurs with serpentine In the Fie.mathul. Tyrol; also at Texas. Penn., and the Bure H iU , Md. OymniU of Thomsou, nam ei from yv/tyoS, naked, iu allusion to the locality at Bare Hills, MU is the same species. ' , Nickel Gyionite. A gymuite with part of the magnesium replaced by nickel. 2Ni0.2MgO.8Si0*.6H,0. Amorphous, with a delicate stnlactiiic surface, incrust- ing. H. = S-4; sometimes very soft. G. = 2-409. Luster res nous. Color i ale applegreen, or yellowish. From Texas, Lancaster Co., Pn., in thin crusts on chromite. G arm ent. Noumeite. Au important ore of nickel, consisting essentially of a hydrated silicate of magnesium and uicke), perhaps H ,(N i.M g)S04 + aq, but very variable m com position, particularly as regards the nickel and magnesium; not always homogeneous Amorphous. Soft and friable. G. = 2 3-2 8. Luster dull. Color bright upple-gieeu pule green to nearly while, lu part unctuous; sometimes adheres to the longue. Occur* tn serpentiue rock near Noumea, capital of New Caledouia, associated with chromic irou and steatite, where it is extensively miutd. A similar ore occurs at Riddle iu Douglua County, southern Oregon; also at Webster, Jackson Co., N. C. TALC. Orthorhombic or monoclinic. Rarely in tabular crystals, hexagonal or rhombic with prismatic angle of 00. Usually foliated massive; sometimes in globular and Btellated groups; also granular massive, coarse or fine; fibrous (pseudomorphous); also compact or cryptocrystalline. Cleavage: basal, perfect. Sectile. Flexible in thin laminae, but not elastic. Percussion-figure a six-rayed star, oriented as with the micas. Feel greasy. H. = l - l o . G. = 2`7-2*8. Luster pearly on cleavage surface. Color applegreen to white, or silvery-white; also greenish gray and dark green; sometimes bright green perpendicular to cleavage surface, and brown and less translucent at right angles to this direction; brownish to blackish green and reddish when impure. Streak usually white; of dark green varieties lighter than the color. Subtransparent to translucent. Optically negative. Ax. pi. jo . Bx J. c. Axial angle small, y -- a = 0 035-0`050. v r --Foliated, Talc. Consists of fol'n, usually easily separated, having a greasy feel and presenting ordinarily light green, greenish white, and white colors. 0 = 2 55-2 78. ' Massive, Steatite or Soapstone (Speckstein Qerm.). a. C'onrse granular, grayish green and brownish gray in color; H. = 1-2 5. Pot stone is ordinary soapstone, more or less impure, b. Fine granulnr nr cryptocrystalltne. and soft enough to be used as chalk; ns the French chalk, which is milk-white with n pearly luster, c. Indurated talc. An impure slaty talc, harder than ordinary talc. Pseudomorphous. a. Fibrous, fine to coarse, altered from pnstntite and tremolite. b. llensselaerite, having the form of pyroxene from northern New York nnd Cannda. Comp.--An acid metasilicate of magnesium ,H, Mg,(SiO,)4or H,0.3M g0.4Si0 = Silica 63-5, magnesia 317, water 4 8 = 100. The water goes off only at a red heat. Nickel is sometimes present in small amount. P y r., etc.--In the closed tube B B., when intensely ignited, most varieties yield water. In the platinum forceps whitens, exfoliates, and fuses with difficulty on the thin edges to a white enamel. Moistened with cobalt solution, assumes on ignition a pale red color. N< t decomposed by acids. Rensselaeiite is decomposed by concentrated sulphuric ncid. Diff --Characterized by extreme softness soapy feel; common foliated structure; pearly luster; it is flexible but inelastic. Yields water only on intense ignition Ob.--Talc or steatite is a very common mineral, and in the latter form constitutes extensive lieds in some teeions. It is often associated with serpentine, tRhoe or chloride schist, and do'omite, and frequently contains crystals of dolomite, bnunnerile, also asbestos, acttnoliie, tourmaline, magnetite. ' Steatite is the material of mnny psendomorphs, among which the most rommnn are those after pyroxene, hornblende, mica, scnpolite, and spinel. The magnesian minerals are 480 DE8CBIPTIVE MINERALOGY. those which commonly afford steatite by alteration; while those like scapoliteand nephelite, which contain soda and no magnesia, most frequently yield pinite-like pseudomorphs. There are also steatltic pseudomorphs after quartz, dolomite, topaz, chiastolite, staurolite, cyanite, garnet, vesuvianite, chrysolite, gehlenite. Talc in the tibrouB form ispseudomorph after enstatite and tremolite, Apple-green talc occurs at Mt. Greiner In the Zillerthal, Tyrol; in the Valais and St Gothard in Switzerland; in Cornwall, near Lizard Point, with serpentine; the Shetland islands. In N. America, foliated talc occurs in Maine, at Dexter. In Vermont, at Bridgewater, handsome green talc, with dolomite; Newfane. In Mass., at Middlefield. Windsor, Blanford, Andover, and Chester. In R. Island, at Smitlifield, delicate green and white in a crystalline limestone. In AT. York, at Edwards, St. Lawrence Co., a fine fibrous talc (agalile) associated with pink tremolite; on Staten Island. In N. Jersey, Bparta. In Penn. at Texas, Nottingham, Unionville; in South Mountain, ten miles south of Carlisle; at Chestnut Hill, ou the Schuylkill, talc and also soapstone, the latter quarried extensively In Maryland, at Cooptown, of green, blue, and row colors. In N. Cur., at Webster, Jack son Co. In Canada, in the townships Bolton, Sutton, and Potion, Quebec, with steatite in beds of Cambrian age; in the township of Elzevir, Hastings Co., Outario, an impure grayish van in Archaean rockB. SE PIO IJT E . Meerschaum Germ. L'cume de mer Fr. Compact, with a smooth feel, and fine earthy texture, or clay-like; also rarely fibrous. H. = 2-2-5. G. = 2. Impressible by the nail. In dry masses floats on water. Color grayish white, white, or with a faint yellowish or reddish tinge, bluish green. Opaque. Comp.--H 4Mg,Si 0 Jt or 2H ,0.2M g0.3Si0, = Silica 60*8, magnesia 27-1, water 12-1 = 100. Some analyses show more water (2HtO), which is probably to be regarded as hygroscopic. Copper and nickel may replace part of the magnesium. P yr., ete.--In the closed tube yields first hygroscopic moisture, sud at a higher temperature gives much water and a burnt smell. B.B. some varieties blacken, then burn white, and fuse with difficulty on the thin edges. With cobalt solution a pink color on ignition. Decomposed by hydrochloric acid with gelatinization. Obs.--Occurs in Asia Minor, in masses in stratified earthy or alluvial deposits at the plains of Eskihi sher; at Hrubechitz in Moravia; in Morocco, called iu French Pierre de Savon de Maroc; at Vallecaa in Spain, In extensive beds. A fibrous mineral, having the composition of sepiolite, occurs in Utah. The word meertchaum is German for eea-froth, oud alludes to its lightness and color. Sepiolite Glocker is from af/ma, cuttle-fish, the bone of which is light and porous; and being also a production of the sea, " deinae spumam marinam siguificuDat," sa>s Glocker. Oonnarite. A hydrous nickel silicate, perhaps HNi1SiiO ,t. In small fragile grains. G. = 2-459-2-619. Color yellowish, greeu. From ROttis, in Saxon Voigtland. Spadaite. Perhaps 5MgO 6S I0,.4H ,0. Maasive, amorphous. Color reddish. From Capo di Bove, near Rome. 8APONITE. Plotine. Massive. In nodules, or filling cavities. Soft, like butter or cheese, but brittle on drying. G. = 2-24-2*30. Luster greasy. Color white, yellowish, grayish green, bluish, reddish. Does not adhere to the tongue. Comp.--A hydrous silicate of magnesium and aluminium; but the material is amorphous and probably always impure, and hence aualyses give no uniform results. Contains SiO, 40-45 p. c., AljO, 5-10 p. c., MgO 19-26 p. c., H tO 19 21 p. c.; also Fe1Ol , FeO, etc. P yr., etc.--B.B. gives out water very readily and blackens; thin splinters fuse with difficulty on the edge. Decomposed by sulphuric acid. Obs.--Occurs in cavities in basalt, dinbase, e tc .; also with serpentine. Thus at Lizard Point, Cornwall, in veins in serpentine; at various localities in Scotland, etc.