Document daKzVpd0OdpvjEVmaRn8MJ3Q

Laboratory Report Cyprus Industrial M inerals Co. Research Division 2435 Military Avenue West Los Angeles, California Telephonei213) 478-0462 Filing No 81-0237 Key Beaverhead ore par tic les References: K. Harris report attached Date of Report 2/22/83 Date of Work Request ' By 12/14/82 M. Kahn Reported 8y Approved By Status P. Col v i l i e/K- Harris P. Colville/'C Comp!ete Copies: Exploration R.S. Lamar T.R. Paul B. Boudress File Samples of hand picked p art ic les logged as talc at the r ig and under binocular microscope were sent fo r examination. Objective Samples were studied by binocular microscope. P ar ti c le s from hole 4054 (25 1--3 0 1, 30 1- 3 5 1s 4 0 1- 4 5 1) are nearly ident ical, pearly l i g h t greenish-grey, rounded, e a s il y scratched with the f in g e rn a il , greasy to the feel and obviously talc. Xray d if f r a c t i o n studies show 95-98% talc. I t i s not immediately obvious from the few p ar ti c le s hand selected why GEB values were so low (64-73). However, a number of the p art ic les were coated with yellow dust. Particles from hole 4052 (130`--1 3 5 ' a 1451--1501, 155' --1601) are irr e g u l a r white fragments that resemble caliche. They break f a i r l y e a si l y . Some can be broken with the fi n g e r n a i l . The powder i s riot pearly or greasy like talc. Xray d if fr a c ti on studies show the hardest white material to be c r i s t o b a l i t e . The presence of c h l o r it e and vermiculite in the assemblage may result in a ground powder that looks and feels l i k e talc. Not all of the white par tic les were pure c r i s t o b a l i t e . Some of the so ft e st ones were chalky mixtures of c a lc i t e , c r i s t o b a l i t e , vermiculite and chlorite. There are s u f f i c i e n t differences so that the two minerals should be i de nt ifi ab le by the core loggers. I am adding some pages out of Dana's mineralogy that give a quick test for MgO. The c r i s t o b a l i t e sample was checked by S.E.M. to see i f i t i s an Opal C-T variety observed in the Tallahasse Creek rocks. The attached report shows that i t is not Opal C-T. The massive c r i s t o b a l i t e occurs with A1 rather than Mg, and the photographs show some development of a clay mineral. This PLAINTIFFS EXHIBIT CAM-44 IT A -A lfa ro 0 0 0 3 6 5 Page 2 Beaverhead Ore was identified as veriniculite by Xray but may be a montmori 11 onite ( b e i d e l li t e ) . Mg was not detected in the samples selected. P. C o l v i l l e PC/mh ITA -A lfaro000366 BEAVERHEAD 1982 Hole #B4054 SAMPLE 10 15 20 -25 -30 35 ty 40 45 50 55 60 65 70 75 80 GEB LOI 56.8 64.4 67.1 69.0 73.3 69.5 55.7 58.6 67.0 61.0 69.0 7.42 5.30 5.02 5.30 5.65 6.73 7.06 7.37 7.80 8.22 11.46 54.1 10.03 TALC <5 tr > 80 > 98 > 95 > 97 > 96 > 89 > 78 > 78 > 74 > 73 > 78 < 30 > 70 CHLORITE > 50 DOLOMITE > 58 < 10 C A L C IT E <5 tr tr tr < 2 <5 <5 < 20 tr < 20 tr < 20 < 5 < 20 < 5 < 5 < 15 < 5 > 43 < 20 < 10 < 10 MICA QUARTZ < 40 < 40 < 10 <2 <5 <2 tr tr tr tr tr <2 <2 <2 FELDSPAR OTHER ' ------------------------- < 10 magnesite 85 69.4 17.64 > 65 < 20 < 15 90 < 40 < 5 > 45 < 5 95 56.0 8.45 > 75 < 20 < 5 <5 100 < 55 < 5 < 10 < 10 < 10 a- 10 serpentine (continued) ITA -A lfaro000368 CHEMICAL EXAMINATION OP MINERALS 369 617. Salt of Phosphorus. -- This flux gives for the most part reactions similar to those obtained with borax. The only cases enumerated here are those which are distinct, and hence those where the flux is a good test. With silicates this flux forms a glass in which the bases of the silicate are dissolved, but the silica itself is left insoluble. It appears as a skeleton readily seen floating about in the melted bead. The colors of the beads, and the metals to whose oxides these are due, are: Color Substance fled ...................... Green................... Y e llo w ................. . Chromium in O.F., h o t-- (fine green when cold). Chromium in O.F. and R.F., when cold -- (red in O F., hot). Molybdenum in K.F., dirty green, hot; fine green, cold -- (yellow-green in O.F.). Uranium in R.F., cold; yellow-green, hot. Vanadium, chrome-green in R.F., cold -- (brownish red, hot). In O.F., dark yellow, hot, paler on cooling. Molybdenum, yellowish green in O.F., hot, paler on cooling -- (in R.F., dirty, green, hot; fine green, cold). Uranium in O.F., hot; yellowish green, cold -- (in R.F., yellowish green, hot: green, cold). . Vanadium in O.F., dark yellow, hot, paler on cooling-- (in R.F., brownish red, hot; chrome-green, cold). Violet................... Titanium (TiO.) in R.F., yellow, hot. (Also in O.F., yellow, hot; color less, cold.) C haracteristic R eactions of the I mportant E lem ents and of S ome of T heir Compounds 518. The following list contains the most characteristic reactions, chiefly before the blowpipe and iu some cases also in the wet way, of the different elements and their oxides. It is desirable for every student to gain familiarity with them by trial with as many minerals as possible. Many of them have already been briefly mentioned in the preceding pages. For a thoroughly full . description of these and other characteristic tests (blowpipe and otherwise) reference should bo made to the volume by Brush and Penfield referred to on p. 361. It is to be remembered that while the reaction of a single substance may be perfectly distinct if alone, the presence of other substances may more or less entirely obscure these reactions; it is consequently obvious that in the actual examination of minerals precautions have to be taken, and special methods have to be devised, to overcome the difficulty arising from this cause. These will be gathered from the " pyrognostic characters " (Pyr.) given in connection with the description of each species in Part V of this work. Aluminum. -- The presence of aluminum in most infusible minerals, containing a con siderable amount, may be detected by the blue color which they assume when, after being heated, they are moistened with cobalt solution and again ignited (<'.<!, kyanite, andalusite, etc.). Very hard minerals (as corundum) must be first finely pulverized. The test is not conclusive with fusible minerals since a glass colored blue by cobalt oxide may be formed. It is to be noted that the infusible calamine (zinc silicate) also assumes a blue color when treated with cobalt nitrate. From solutions aluminum will lie precipitated as a llocculent white or colorless precipitate on the addition of ammonium hydroxide in excess. Antimony. -- Antimnnial minerals roasted on charcoal give dense white odorless fumes; metallic antimony and its sulphur compounds give in the open tube a white sublimate of oxide of antimony fsce p. hiin). Antimony sulphide (stibniteh also many sulphantimonites, give in a strong heat in the closed tube a sublimate of antimony o.yvsulphide, black when hot, brown-red when cold. Gives iodide test on plaster, orange to reel. Sublimate disapjiears when subjected to ammonia fumes. See also p. 3l>7. CHEMICAL MINERALOGY acid1" nitr'C add' comP'ltK,s containing antimony deposit white insoluble metantimonic u su ^ h ^ Whe" r f 1 n c lT O l1 ' gviovleastilae,sucbrlyimstaaltleindearskubblrimowante-reodf A*rsnenihc ^n rf iTi ^i t i In^tthliep'crlloos^e'di tubf ethaerysegnli.vcesaulphide and some arsenides yield a black to grav mirror if mnt ' ,s 1 J^low when cold; arsenic arsenates the arsenic can be detected bv the smrlic Jrl * le t`,os.etl tube- In powdered mineral with charcoal dust and c-,d'S' 10 ! o r? le,lied when a mixture of the 0F the^ 's o /? ' ' hC,U;ed tUi,e > `'r'S obtafn^^ftw^nte^^ign^Uon UI^*Sa^3' excePt d d u S p iu 5 c a c eid.by the he"Vy " h L Pracipitate (BaSOj) to ammonia fumes ~ g Cd' ChanSes to orange-yellow and red on exposure with one part powdered fluorite and two n , K IS t, fbe powdered mineral moistened and placed on plarinum w c A t t h e Z TM ? T f b!s,,Il?',ate- The fixtu re is but lasts but an instant. At the moment oi {uslon the green color appears, turmeric paper*wtoclfhas been ^ i^ t e n ^ with R^nd the*1 f VC? n m ! ishul,ro'''n color to to black when ammonia is ^ ur" i on the paper thCQ dncd at 100" tho lor changes on turmeTe ^ p e f e t e i n g S f sulphates, etc.) - alkaline reaction ammonTmkloxalidte0r addition of sulphuric acid " oxalate by the addition of P " 13 Precipitated in concentrated solutions only on ^ s s i S S S S ' i fgM S fs In solution chlorine gives with silver nit rate >white tll',rp lsb f!ilme ot Copper chloride, winch darkens in color on exposure to the ' curdv precipitate of silver chloride soluble in ammonia. ure to the light, it is insoluble in nitric acid, but entirely y e l f e b o r a x a bead which fO.F.) is yellow to red (hot) and the bead is dirty creen (hot) and ,.2 e,ncra^ "With salt of phosphorus in O.F. bcyon^faL^p|;y3G8 3G0) g d dear rcen (ral`l;; "> K.F. the same. Cf. vanadium containing rntail^^Vherc sidi!hi'?r ' 3 obtained w`th borax in Ixith flames from minerals ougldy roasted on charcoal ` OT arseme 13 I'r cn t the mineral should first be thor? its eompoii, 11!s^"In*thecaseHf su*iphh!esthe TMpI,er c?n .1>c educed from most of opaipic red U , K S B CuJ' 'l , X T c P 1 T V *0 ^ '! ^ " ^ T a n moistening i|l<; mineral with hv^hoe or 1 achl f n ' rCo,ppi:r| 'blonde, oblained by be previously roasted) yields a vivid -mmo b e bn ^ "drii tl,e "'incral should . . Most metallic compounds are soluble in mtr c ! .CTnf,n Ic ?1VPS a Km'" Hame. intense blue cuior ^ the solution. ,tnL `ltJ,d- Ammonia in excess produces an 00370 mm CHEMICAL EXAMINATION OF MINERALS 371 Fluorine. -- Heated in the closed tube with potassium bisulphatc and powdered class produces a white sublimate of SiO;. This sublimate and the hydrofluosihcic acid present form a volatile combination. But it the lower end of the tube is broken off arid the open t Jbe then dipped in a test tube of water so that the acid is removed, the deposit of 01O2 which will appear when the tube is dried will be found to be no longer volatile. Heated gently in a platinum crucible with sulphuric acid, many compounds le.q., fluorite) give off hydrofluoric acid, which corrodes the exposed parts of a glass plate placed over it which has been coated with wax and then scratched. Iron. -- Minerals which contain even a small amount of iron yield a magnetic mass when heated in the reducing flame. With borax iron gives a bead (O.F.) which is yellow to brownish red (according to quantity) while hot, but is colorless to yellow on cooling, R.F. becomes bottle-green (see p. 30S). Ferric iron is precipitated from a solution by the addition of ammonium hydroxide in excess as red-brown ferric hydroxide re(Orl)3. Ferric iron in hydrochloric aciil solution gives deep blue precipitate when potassium ferrocyanide is added; a similar test is obtained for ferrous iron by the addition of potassium Lead. ---With soda on charcoal a malleable globule of metallic lead is obtained from lead compounds; the coating hits a yellow color near the assay; the sulphide gives also a white coatin" (PbSOi) farther off (p. 3CC). On being touched with the reducing flame the coating disappears, tingeing the flame azure-blue. On plaster, lead iodide coating is chrome-yellow. In solutions dilute sulphuric acid gives a white precipitate of lead sulphate; when delicacy is required an excess of the acid is added, the solution evaporated to dryness, and water added; the lead sulphate, if present, will then be left as a residue. Lithium. -- Lithium gives an intense carmine-red to the outer flame, the color somewhat resembling that of the strontium flame but deeper; in very small quantities it is evident in the spectroscope. , ..... j . . , ., Magnesium. -- Moistened, after heating, with cobalt nitrate and again ignited, a pink color is obtained from some infusible compounds of magnesium (e.g* brucite). In solution the addition of ammonium hydroxide in large excess and a little hydrogen sodium phosphate iroduces a white granular precipitate of NfiMgPO.i. Elements precipitated by ammonium iydroxide or ammonium oxalate should be removed first. . Manganese. -- With borax manganese gives a bead violet-red (O.F.), and colorless (R.h With soda (O.F.) it gives a bluish green bead; this reaction is very delicate and may be relied upon, even in presence of almost any other metal. Mercury. -- In the closed tube a sublimate of metallic mercury is yielded when the mineral is heated with dry sodium carbonate. In the open tube the sulphide gives a mirror of metallic mercury; in the closed tube a black lusterless sublimate of HgS, red when rubbed, is obMtaoilnybedde.num. -- On charcoal mo.ly.b.denum su,lp,hi.d. e gives near the assay a copper-red, stain (O F ). and beyond a white coating of the oxide; the former becomes azure-blue when for a moment touched with the ILF. The iodide coating on plaster is deep u tramanne blue. The salt of phosphorus bead (O.F.) is yellowish green (hot) and nearly colorless (cold) ; also fR.F.) a fine green. Molybdates are tested by putting powdered mineral in dry test tube with small scrap of paper, adding a few drops of water and an equal amount of concentrated sulphuric acid. Heat until acid fumes, Cool or add slowly drops of water and solution will assume deep blue color. , .. . . ,, Nickel. -- With borax, nickel oxide gives a bead which (O.F.) is violet when hot and red brown on cooling; (ILF.) the glass liccomes gray and turbid from the separation of metallic nickel. A solution of nickel becomes pale blue (cf. copper) on the addition of ammonia in excess. If an alcoholic solution of dimcthylglyoxine is added, to an ammomacal solution a scarlet precipitate is formed. .. . ,, , Niobium (Coluinbium). -- An acid solution boiled with metallic tin gives a blue color which slowly changes to brown on continued boiling and disappears on dilution. The reac tions with the fluxes are not very satisfactory. ,, . Nitrates. -- These detonate when heated on charcoal. Ileated in a tube with sulphuric acid thev give off red fumes of nitrogen dioxide (NO;). Phoeyhrmm. -- Most phosphates impart a green color to the flame, especially after having been moistened with sulphuric acid, though this test may lie rendered unsai factory by the presence rif other coloring agents. If they are fused in the closed tube villi a fragment of metallic magnesium or sodium, and afterward moistened with water, phosplmreted hydrogen is given olf, recognizable by its disagreeable odor. A few 1Imps of a nitric acid solution, containing phosphoric acid, produce in a solu tion of ammonium molybdate a pulverulent yellow precipitate of ammonium phijspho- molybdulc. 3371 372 CHEMICAL, MINERALOGY Potassium. -- Potash imparts a violet color to the flame when alone. The flame is best observed through a blue glass filter which will eliminate the sodium flame color which will almost invariably be present. It is best detected in small quantities, or when soda or lithia is present, by the aid of the spectroscope. See also p. 301. Selenium. -- On charcoal selenium fuses easily, giving off brown fumes with a peculiar disagreeable organic odor; the sublimate on charcoal is volatile, and when heated (R.F.) gives a fine azure-blue flame. On plaster gives red to crimson volatile sublimate with char acteristic odor. Silicon. -- A small fragment of a silicate in the salt of phosphorus bead leaves a skeleton of silica, the bases being dissolved. Most silicates are insoluble in acids. The fine powder of such a silicate is fused with sodium carbonate and the mass then dissolved in hydrochloric acid and evaporated to dry ness, the silica separates as a gelatinous mass and on evaporation to dryness is made insol uble. When strong hydrochloric acid and then water is added to the dry residue in the test tube, the bases are dissolved and the silica left behind. Manv silicates are directly soluble in hydrochloric acid, and the solution on evaporation will yield the characteristic silica jelly. Other silicates when treated with acid are decom posed, the bases present going into solution, but the silica separating and remaining sus pended in the liquid. There are gradations between these three groups. Silver. -- On charcoal in O.F. silver gives a brown coating. A globule of metallic silver may generally be obtained by heating on charcoal in R.F., especially if soda is added. Uncler some circumstances it is desirable to have recourse to cupellation. From a solution containing any salt of silver, the insoluble chloride is thrown down when hydrochloric acid is added. This precipitate is insoluble in acid or water, but entirely so in ammonia. It changes color on exposure to the light. Strontium. -- Compounds of strontium are usually recognized by the fine crimson-red which they give to the blowrpipe flame; many yield an alkaline reaction after ignition (cf. barium). In concentrated and slightly diluted solutions strontium sulphate will be precipitated on the addition of sulphuric acid (cf. calcium and barium). Sodium. -- Compounds containing sodium give a strong and persistent yellow flame. Some compounds will give an alkaline reaction after ignition. Sulphur, Sulphides, Sulphates. -- In the closed tube some sulphides give off sulphur; in the open tube they yield sulphur dioxide, which has a characteristic odor and reddens a strip of moistened litmus paper. In small quantities, or in sulphates, sulphur is best detected by fusion on chareoal with soda and charcoal dust. The fused mass, when sodium sulphide has thus been formed, is placed on a clean silver coin and moistened; a distinct black stain on the silver is thus obtained (the precaution mentioned on p. 307 must be exercised). A solution of a sulphate in hydrochloric acid gives with barium chloride a white insoluble precipitate of barium sulphate. Tellurium. -- Tcllurides heated in the open tube give a white or grayish sublimate, fusible to colorless drops fp. 305). On chareoal they give a white coating and color the R.F. green. On plaster they give a dark brown volatile sublimate. A small amount dis solved in warm concentrated sulphuric acid vields a deep red solution. The color will disappear if acid is heated too hot or if on cooling, water is added. Tin. -- Minerals containing tin (e.g., cassiteritc), when heated on charcoal with soda or potassium cyanide, yield metallic tin in minute globules and a white anti difficultly volatile oxide coating is formed; the globules are malleable, but harder than silver. Dissolved in nitric acid, white insoluble stannic oxide separates out. Titanium. -- Titanium gives in the U.F, with salt of phosphorus a bead which is violet when cold. Fused with sodium Carbonate and dissolved in hydrochloric acid, and heated with a piece of metallic tin, the liquid takes a violet color, especially after partial evaporation. A yellow to amber color results when hydrogen [teroxide is added to a sul phuric acid solution. Tungsten. -- Tungsten oxide gives a blue color to the salt of phosphorus liead (R.F ). Fused and treated as titanium (see above) with the addition of zinc instead of tin, gives a fine blue color. The color changes to brown on continued reduction. The color does not disappear when the solution is diluted (cf. niobium). Uranium. -- Uranium compounds give to the salt of phosphorus bead (O.F.) a greenish yellow bead when cool; also (R.F.) a tine green on cooling (p. 309). Vnnadium. -- With borax ((t.l'.J vanadates give a head yellow (hot) changing to yellow ish green and noarlv colorless (cold i; also (R.F.) dirty green (hot), line green (coldl. \\ ith salt `it' phosphorus (O F.) a yellow to amber color (thus differing from chromium); also (R.F.) fine green (cold). ' ^AtlafaKruos0it0iM03B7 2 CHEMICAL EXAMINATION OF MINERALS 373 Zinc. -- On charcoal in the reducing flame compounds of zinc give a coating which is yellow while hot and white on cooling, and moistened by the cobalt solution and again heated becomes a fine green. Note, however, that the zinc silicate (calamine) becomes blue when heated after moistening with cobalt solution. Zirconium. A dilute hydrochloric acid solution, containing zirconium, imparts an orange-yellow color to turmeric paper, moistened by the solution. D eterminative M ineralogy 519. Determinative Mineralogy may be properly considered under the general head of Chemical Mineralogy, since the determination of minerals depends mostly upon chemical tests. But crystallographic and all the physi cal characters have also to be carefully observed. _ There is but one exhaustive way in which the identity of an unknown mineral may in all cases be fixed beyond question, and that is by the use of a complete set of determinative tables. By means of such tables the mineral in hand is referred successively from a general group into a more special one, until at last all other species have been eliminated, and the identity of the one given is beyond doubt. A careful preliminary examination of the unknown mineral should, how ever, always be made before final recourse is had to the tables. This examina tion will often suffice to show what the mineral in hand is, and ip any case it should not be omitted, since it is only in this way that a practical familiarity with the appearance and characters of minerals can be gained. The student will naturally take note first of those characters which are at once obvious to the senses, that is: crystalline form, if distinct; general struc ture, cleavage, fracture, luster, color (and streak), feel; also, if the specimen is not too small, the apparent weight will suggest something as to the specific gravity. The characters named are of very unequal importance. Structure, if crystals are not present, and fracture are generally unessential except in distinguishing varieties; color and luster are essential with metallic, but generally very unimportant with nonmetallic minerals. Streak is of impor tance only with colored minerals and those of metallic luster (p. 271). Crys talline form and cleavage are of the highest importance, but may require careful study. The first trial should be the determination of the hardness (for which end the pocket-knife is often sufficient in experienced hands). The second trial should be the determination of the specific gravity. Treatment of the pow dered mineral with acids may come next; by this means (see pp. 359, 3G0) a carbonate is readily identified, and also other results obtained. Then should follow blowpipe trials, to ascertain the fusibility; the color given to the flame if any; the character of the sublimate given off in the tubes and on charcoal' the metal reduced on the latter; the reactions with the fluxes, and other points as explained in the preceding pages. How much the observer learns in the above way, in regard to the nature of his mineral, depends upon his knowledge of the characters of minerals in general, and upon his familiarity with the chemical behavior of the various elementary substances with reagents and before the blowpipe (pp. .'J.jff to 309). If the results of such a preliminary examination are sufficiently definite to suggest lhat the mineral in hand is one of a small number of species, reference may be made to their full description in Part V' of this tvork for the final decision. Laboratory Report Cyprus Industrial M inerals Co. Research Division 2435 M ilitary Avenue Wes! Los Angeles, Calilorma Telephone (21 3) 478-0462 Filing No References. Key Beaverhead ore particles Date of Report 2/21/83 Date ot Work Request ' By 1 2 /1 4 /8 2 M, Kahn Reported By ^ H a rris Approved By p> Status S.E.M. Complete Exploration R. S. Lamar T. R. Paul B. Boudress File Samples of Beaverhead pa r ti c le s logged at r ig as having abundant talc. Objective S.E.M. examination to obtain micrographs and Xray analysis. Results: Several hand picked par tic les were examined in S.E.M. and EDAX spectrums were taken. Micrographs were taken at X5Q00 and X10000 of samples from the 145 1-150 1, and 155 1-160 1 levels of hole No. 4052. EDAX spectrums did not show the presence of Mg. Micrographs and EDAX spectrum included. K. L. Harris KLH/hks ITA-Alfaro000374 Page 2 Beaverhead ore particles R: & RVRHRb 033 0 2 0 3 _______i__________________________________ . -.. J ] ................... ................................................... -- - - ---- iiTHQ mm fl S LI A -- -- -- C R ITA-Alfaro000375 Page 3 Beaverhead ore particles ITA-Alfaro000376 Page 4 Beaverhead ore particles ITA-Alfaro000377 Page 5 Beaverhead ore particles ITA-Alfaro000378 Phyllosilicates EENS2110 Mineralogy Tulane University Prof. Stephen A. Nelson Phyllosilicates (Micas, Chlorite, Talc, & Serpentine) This document last updated on 08-Nov-2010 Phyllosilicates (Sheet Silicates) The phyllosilicates, or sheet silicates, are an important group of minerals that includes the micas, chlorite, serpentine, talc, and the clay minerals. Because of the special importance of the clay minerals as one of the primary products of chemical weathering and one of the more abundant constituents of sedimentary rocks, they will be discussed in more detail in the next lecture. The basic structure of the phyllosilicates is based on interconnected six member rings of Si04"4 tetrahedra that extend outward in infinite sheets. Three out of the 4 oxygens from each tetrahedra are shared with other . -j tetrahedra. This leads to a basic structural unit of Si2Os Most phyllosilicates contain hydroxyl ion, OH", with the OH located at the center of the 6 membered rings, as shown here. Thus, the group becomes Si70 5(0H)"3. When other cations are bonded to the Si04 sheets, they share the apical oxygens and the (OH) ions which bond to the other cations in octahedral coordination. This forms a layer of cations, usually Fe+2, Mg+2, or Al+3, that occur in octahedral coordination with the O and OH ions of the tetrahedral layer. As shown, here, the triangles become the faces of the octahedral groups that can bind to the tetrahedral layers. The octahedral layers take on the structure of either Brucite [Mg(OH)3], if the cations are +2 ions like Mg~2 or Fe+2, or Gibbsite [Al(OH)3], if the cations are +3 like Al+3. In the brucite structure, all octahedral sites are occupied and all anions are OH'1. In the Gibbsite structure every 3rd cation site is unoccupied and all anions are OH"1. Page 1 of 7 ITA-A lfaro000379 Phyllosilicates This gives rise to 2 groups of sheet silicates: 1. The trioctahedral sheet silicates where each O or OH ion is surrounded by 3 divalent cations, like Mg+2 or Fe+2. 2. The dioctahedral sheet silicates where each O or OH ion is surrounded by 2 trivalent cations, usually Al+3. We can build the structures of the various sheet silicates by starting with the octahedral layers similar to the structures of brucite or gibbsite, as shown below. The trioctahedral phyllosilicates are based on the structure where the octahedral layers are similar to brucite, where Mg-2 occupies the cation position. Trioctahedral Brucite Mg(OH)3 Dioctahedral Gibbsite AI(OH)3 The dioctahedral phyllosilicates are based on the structure where the octahedral layers are similar to gibbsite, where Al+3 occupies the cation position. The octahedral sheets in both cases are held together by weak Van der Waals bonds. If we start with the brucite and gibbsite structures shown above, and replace 2 of the OH ions with O, where the Oxygens are now the apical Oxygens of the tetrahedral sheets, then we get the structure of the serpentine mineral, Lizardite, if the octahedral layer is trioctahedral, containing Mg+2. If the octahedral layer is dioctahedral, containing Al ~3, the structure of the clay mineral Kaolinite, is obtained. Trioctahedral Lizardite Mg2Si20 5(0H)4 Dioctahedral Kaolinite AIjS^OstOH)^ This leads to a tetrahedral - octahedral (T-O) structure, where each T-0 layer is bonded to the top (or bottom) o f another T-0 layer by Van der Waals bonds. Trioctahedral Dioctahedral If 2 more of the OH ions in the octahedral Talc Mg5Si4G10(OH)2 layer are replaced by O, and these O become the apical Oxygens for another tetrahedral layer, the this builds the trioctahedral phyllosilicate talc or the dioctahedral pyrophyllite. This becomes a T-O-T layer that can bond to other T-O-T layers by weak Van der Waals bonds. Pyrophyllite AI2S.4O10(OH)2 oo O OH' o Mg*! o AT' * SI"1 Page 2 o f 7 ITA-Alfaro000380 Phyllosilicates If an Al+3 is substituted for every 41*1Si+4 in the tetrahedral layer, this causes an excess -1 charge in each T-O-T layer. To satisfy the charge, K+1 or Na 1can be bonded between 2 T-OT sheets in 12-fold coordination. Trioctahedral Phlogopile KMg3A(SisQia{QH)2 Dioctahedral Muscovite KAI2AISi3Oia(OH)2 oo e oh' o Mi" A3 . Si'4 For the trioctahedral sheet silicates this becomes Phlogopite (Mg-biotite), and for the dioctahedral sheet silicates this becomes Muscovite. This makes a T-O-T - T-O-T layer that, again can bind to another T-O-T - T-O-T layer by weak Van der Waals bonds. It is along these layers of weak bonding that the prominent {001} cleavage in the sheet silicates occurs. Replacing 2 more Si+4 ions with Al+3 ions in the tetrahedral layer results in an excess -2 charge on a T-O-T layer, which is satisfied by replacing the K-1 with Ca^2. Trioctahedral Clintonile CaMg3AI2Si2Of0(OH}2 Dioctahedral Margarite CaAI2AI2Si2O10(OH)2 This results in the trioctahedral sheet silicate - Clintonite and the dioctahedral sheet silicate Margarite. Because of the differences in charge balance between the trioctahedral and dioctahedral sheet silicates, there is little solid solution between the two groups. However, within the trioctahedral sheet silicates there is complete substitution of Fe for Mg and limited substitution of Mn+2 into the octahedral sites. Within the dioctahedral sheet silicates there is limited substitution of Fe-3 for Al+J in octahedral sites. In addition, F" or CP can substitute for (OH)' in the hydroxyl site. As previously discussed, substitution of F '1 stabilizes the mineral to higher pressures and temperatures. Another group of phyllosilicates that is more of mixture of structural types is the chlorite group. Although chlorite is complex in that the amount of A1 that can substitute Mg and Si is Page 3 of 7 ITA-Alfaro000381 Phyllosilicates variable, one way of looking at the chlorite structure is shown below. Chlorite (Mg5Al)(Si3Al>0f0(0 H)a Here, the chlorite structure is depicted as consisting of a brucite-like layer (with some Al) sandwiched between tetrahedral layers that are similar to phlogopite. Another important sheet silicate structure is that of vermiculite. This is similar to the talc structure, discussed above, with layers of water molecules occurring between each T-O-T layer. Similarly, insertion of layers of water molecules between the T-O-T sheets of pyrophyllite produces the structure of smectite clays. The vermiculite and smectite groups are therefore expanding type sheet silicates and as the water is incorporated into the structure the mineral increases its volume. Although we have shown that the octahedral layers fit perfectly between the tetrahedral layers, this is an oversimplification. If the tetrahedral layers were stacked perfectly so that apical oxygens were to occur vertically aligned, then the structure would have hexagonal symmetry. But, because this is not the case, most of the phyllosilicates are monoclinic. Serpentine Group The serpentine group of minerals has the formula - Mg-jSi70 5(0H)4. Three varieties of serpentine are known. Antigorite and Lizardite are usually massive and fine grained, while Chrisotile is fibrous. As discussed above, the imperfect fit of the octahedral layers and the tetrahedral layers causes the crystal structure to have to bend. In Antigorite the bending of the sheets is not continuous, but occurs in sets, similar to corrugations, as shown Tetrahedral Layers here. Octahedral Layers Antigorite Page 4 of 7 ITA-Alfaro000382 Phyllosilicates In Chrisotiie, the bending of the sheets is more continuous, resulting in continuous tubes that give the mineral it's fibrous habit. The Chrisotiie variety is commonly referred to as asbestos. Chrisotiie Occurrence - Serpentine is found as an alteration product of Mg-rich silicates like pyroxene and olivine. It results due to hydration. For example: 2Mg2S i04 + 3H20 <=> Mg3Si20 5(0H )4 + Mg(OH)2 Olivine water Serpentine Brucite Thus, serpentine is commonly found pseudomorphed after olivines and pyroxenes in altered basic and ultrabasic igneous rocks, like altered peridotites, dunites, and sometimes basalts and gabbros. It is commonly associated with minerals like magnesite (MgC03), chromite, and magnetite. If the rock is made up almost entirely of serpentine, it is called a serpentinhe. Properties - Because the serpentines usually occur either as fine-grained aggregates or fibrous crystals, optical properties are difficult to determine. Most of the time, serpentine can be distinguished by its characteristic pseudomorphing of other crystals like olivines and pyroxenes. In hand specimen it generally tends to have a dark green color with a greasy luster. In thin section it is clear to pale green to pale yellow, but does not show pleochroism, shows a generally low relief compared to minerals like olivine and pyroxene with which it is associated, and show very' low order interference colors due to its low birefringence. Talc Talc has the chemical formula - Mg3Si4O 10(OH)2. It is probably best know for its low hardness. Although it has a micaceous structure, it is so easily deformed, that crystals are rarely seen. Occurrence - Like serpentine, talc requires an environment rich In Mg. It is therefore found in low grade metamorphic rocks that originated as ultrabasic to basic igneous rocks. Rocks composed almost entirely of talc have a greasy feel and are referred to as soapstone. Properties - Talc is most easily distinguished in hand specimen by Its lowrhardness, greasy feel, and association with other Mg-bearing minerals. When crystals are present they show the characteristic micaceous cleavage on {001}. In thin section, talc is colorless, biaxial negative with a 2V of 0 to 30. Like other sheet silicates, it shows the well developed {001} cleavage. Maximum interference colors, consistent with a birefringence of 0.05 is 3 yellow. Muscovite has a higher birefringence and higher 2V, properties which easily distinguish the 2 minerals. Page 5 of 7 ITA-Alfaro000383 Phyllosilicates Mica Group The micas can be divided into the dioctahedral micas and the trioctahedral micas, as discussed above. Muscovite, Paragonite, and Margarite are the white micas, and represent the trioctahedral group, and Biotite and Clintonite (Xanthophyllite) the black or brown mica, represents the dioctahedral group. Muscovite and Biotite are the most common micas, but the Lithium- rich, pink mica, Lepidolite, K(Li,Al)2AlSi3O 10(OH)2 is also common, being found mostly in pegmatites. Muscovite Muscovite, KAl3Si3O 10(OH)2, and Paragonite, NaAl3Si3O 10(OH)2, are two potential end members of the solid solution series involving K and Na. But, there is a large miscibility gap between the two end members with Muscovite being between 65% and 100% of K-rich end member, and Paragonite showing compositions between about 80% and 100% of the Na-rich end member. Occurrence - Muscovite is common constituent of Al-rich medium grade metamorphic rocks where is found in Al-rich schists and contributes to the schistose foliation found in these rocks. Muscovite is also found in siliceous, Al-rich plutonic igneous rocks (muscovite granites), but has not been found as a constituent of volcanic rocks. In these rocks it is commonly found in association with alkali feldspar, quartz, and sometimes biotite, garnet, andalusite, sillimanite, or kyanite. Properties - Muscovite is easily identified in hand specimen by its white to sometimes light brownish color and its perfect {001} cleavage. In thin section, the {001} cleavage is easily seen and it's high birefringence is exhibited by the large change in relief on rotation of the stage and it's 2nd to 4th order interference colors. It is clear and shows no pleochroism (which distinguishes it from Biotite), and it is biaxial negative with a 2V between 28 and 50. One of the most diagnostic properties of the micas, including muscovite, is the mottled or birds-eye extinction exhibited by these minerals. Biotite Biotite is a solid solution between the end members Phlogopite KMg3AlSi3O 10(OH)2 and Annite KFe3AlSi30]Q(0IT)2'although pure Annite does not occur in nature. In addition, small amounts of Na, Rb, Cs, and Ba may substitute for K, and like in other minerals, F can substitute for OH and increase the stability of Biotite to higher temperatures and pressures. Occurrence - Nearly pure phlogopite is found in hydrous ultrabasic rocks like kimberlite, and is also found in metamorphosed dolomites. Biotite, with more Fe-rich compositions is common in dacitic, rhyolitic, and trachytic volcanic rocks, granitic plutonic rocks, and a wide variety of metamorphic rocks. In metamorphic rocks, biotite usually shows a preferred orientation with its {001} forms parallel to the schistose foliation. Properties - In hand specimen, Biotite is brown to black and shows the perfect {001} micaceous cleavage. In thin section, it shows the perfect cleavage and mottled extinction Page 6 of 7 ITA-Alfaro000384 Phyllosil cates typical of all micas. It's most characteristic property is its pleochroism, showing yellow to brown to green colors. Hornblende shows similar pleochroic colors, but is distinguished from biotite by the differences in cleavage of the 2 minerals. Biotite is biaxial negative with a low 2V of 0 to 25. Chlorite Group As discussed above, the Chlorite group has a structure that consists of phlogopite T-O-T layers sandwiching brucite-like octahedral layer. There is substantial substitution of Mg for Fe, and A1 can substitute for (Mg, Fe) in both the octahedral sites, as well as for Si in the tetrahedral sites. Thus, chlorite can have a rather complicated formula - (Mg,Fe,Al)3(Si,Al)4O 10(OH)6. Occurrence- Chlorite is a common mineral in low grade metamorphic rocks, where it occurs in association with minerals like actinolite, epidote, and biotite. It also forms as an alteration product of pyroxenes, amphiboles, biotite, and garnet in igneous as well a metamorphic rocks. Properties - In hand specimen, chlorite is recognized by its green color, micaceous habit and cleavage, and association with other minerals like actinolite and epidote. In thin section, Chlorite shows low relief and low birefringence, with a characteristic midnight blue to black anomalous interference color. It shows some pleochroism in the range of green to pale yellow. It is easily distinguished from biotite by its lower relief and anomalous interference color. Examples of questions on this material that could be asked on an exam (note that properties that distinguish different minerals will be included in the laboratory' exam) 1. What is the difference between the dioctahedral and trioctahedral sheet silicates? 2. What is the difference between antigorite and chrysotile? 3. State whether each of the following minerals would be most commonly found in igneous rocks, metamorphic rocks, or both igneous and metamorphic rocks: (a) Chlorite, (b) biotite, (c) muscovite, (d) talc, (e) serpentine, Return to EENS 2110 Page Page 7 of 7 ITA-A lfa r o 3 8 5