Silikatlar Descriptive Mineralogy ( silicate minerals ) › classified on basis of silicate frameworks › basic building unit › TO 4 tetrahedron › T › usually Si 4+ or Al 3+ › 4 O 2- at four corners › degree of polymerization › determined by # of O 2- per TO 4 › shared by adjacent TO 4 tetrahedra DESCRIPTIVE MINERALOGY (SILICATE MINERALS)› degree of polymerization › determined by # of O 2- per TO 4 › shared by adjacent TO 4 tetrahedra› degree of polymerization › determined by # of O 2- per TO 4 › shared by adjacent TO 4 tetrahedra •[SiO 4 ] 4- Independent tetrahedra Nesosilicates •Examples: olivine garnet •[Si 2 O 7 ] 6- Double tetrahedra Sorosilicates •Examples: lawsonite •n[SiO 3 ] 2- n = 3, 4, 6 Cyclosilicates •Examples: beryl Be 3 Al 2 [Si 6 O 18 ]Silicates are classified on the basis of Si-O polymerism •[SiO 3 ] 2- single chains Inosilicates [Si 4 O 11 ] 4- Double tetrahedra •pryoxenes pyroxenoids amphibolesSilicates are classified on the basis of Si-O polymerism •[Si 2 O 5 ] 2- Sheets of tetrahedra Phyllosilicates •micas talc clay minerals serpentineSilicates are classified on the basis of Si-O polymerism low-quartz •[SiO 2 ] 3-D frameworks of tetrahedra: fully polymerized Tectosilicates •quartz and the silica minerals (feldspars, feldspathoids, zeolites)I. NESOSILICATES I. NESOSILICATES ? ?ORTHOSILICATES ORTHOSILICATES › simplest case of TO 4 distribution › no shared O 2- › a monomer › Oli group, Gar group, and the alumino-silicate polymorphsOLIVINE GROUP › general formula › M 2 TO 4 › divalent cations in various proportions › M octahedral-site Fosterite (Fos)M g 2 SiO 4 Fayalite (Fay)F e 2 SiO 4 Tephroite (Tep)M n 2 SiO 4 Monticellite (Mont) CaMgSiO 4 Kirschteinite (Kir) CaFeSiO 4 Glaucochroite (Gla) CaMnSiO 4 Knebelite (Kne) FeMnSiO 4 Larsenite (Lar) PbZnSiO 4 CHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES Crystal Structure and Composition Crystal Structure and Composition › Oli group › isolated silica tetrahedral › general formula › M 2 TO 4 › M › occupied by divalent cations › 6-fold octahedral › Mg 2+ (0.72 Å), Fe 2+ (0.78 Å) and Mn 2+ (0.83 Å) › T › 4-fold tetrahedral site › exclusively by Si 4+ cationCHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES Crystal Structure and Composition Crystal Structure and Composition › Oli group › isolated silica tetrahedral › general formula › M 2 TO 4 › M › occupied by divalent cations › 6-fold octahedral › Mg 2+ (0.72 Å), Fe 2+ (0.78 Å) and Mn 2+ (0.83 Å) › T › 4-fold tetrahedral site › exclusively by Si 4+ cation Olivine (100) view blue = M1 yellow = M2 Olivine (100) view blue = M1 yellow = M2 Olivine (100) view blue = M1 yellow = M2 Olivine (100) view blue = M1 yellow = M2Olivine (001) view blue = M1 yellow = M2 Olivine (001) view blue = M1 yellow = M2 M1 in rows M1 in rows and share and share edges edges M2 form M2 form layers in a layers in a- -c c that share that share corners corners Some M2 Some M2 and M1 and M1 share edges share edgesOlivine (100) view blue = M1 yellow = M2 Olivine (100) view blue = M1 yellow = M2› common SSS › Ca 2 SiO 4 -Mg 2 SiO 4 -Fe 2 SiO 4 diagram › complete solid solution › Fos (Mg 2 SiO 4 ) - Fay (Fe 2 SiO 4 ) - Tep (Mn 2 SiO 4 ) › Mont (CaMgSiO 4 ) - Kir (CaFeSiO 4 ) › Tep › rare (only in metamorphosed Mn-rich sed. rock) › Fos-Fay SS › most common in ign. and met. rocksHardness H Oli =6.5 ›7.0. Specific Gravity SG Fos =3.21; SG Fay =4.10 Colour Oli: green, olive-green, brownish, grayish red, grayish green, yellowish brown, red. Streak Oli: white ›yellowish Luster Oli: vitreous Tenacity Oli: brittle Cleavage Oli: rather distinct Fracture Oli: conchoidal Other Physical Properties Oli: crystals often flattened, massive, compact, granular, transparent ›translucentGARNET GROUP › general formula › (M2) 3 (M1) 2 T 3 O 12 › T-sites › Si +4 › octahedral sites (M1) › Al 3+ , Fe 3+ and Cr 3+ › cubic-sites (M2) › Mg 2+ , Fe 2+ , Mn 2+ and Ca 2+ Pyralspite Garnets Pyrope (Pyr)M g 3 Al 2 Si 3 O 12 Almandine (Alm)F e 3 Al 2 Si 3 O 12 Spessartine (Spes)M n 3 Al 2 Si 3 O 8 Ugrandite Garnets Uvarovite (Uva)C a 2 Cr 2 Si 3 O 12 Grossularite (Gros)C a 3 Al 2 Si 3 O 12 Andradite (Andr)C a 3 Fe 2 Si 3 O 12 Shorlomite (Sho)C a 3 (Fe,Ti) 2 [(Si,Ti)O 4 ] 3 Hydrogrossular (Hgro)C a 3 Al 2 Si 2 O 8 (SiO 4 ) 1-m (OH) 4m where, m=0 ›1CHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES Crystal Structure and Composition › tetrahedra › independent groups › linked to › trivalent ions in M1-sites with a 6-fold coord. › divalent metal ions in M2-sites with 8-fold cubic coord. in interstices wth Si-Al network, each divalent ion being surrounded by 8 O 2- Garnet (001) view blue = Si purple = A turquoise = BCHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES Crystal Structure and Composition › tetrahedra › independent groups › linked to › trivalent ions in M1-sites with a 6-fold coord. › divalent metal ions in M2-sites with 8-fold cubic coord. in interstices wth Si-Al network, each divalent ion being surrounded by 8 O 2- Garnet (001) view blue = Si purple = A turquoise = B Garnet (001) view blue = Si purple = A turquoise = B› complete solid solution btw › pyralspite Gar’s except btw Pyr and Spes › ugrandite Gar’s › complete btw Gros and Andr › limited btw Gros-Andr and pyralspite Gar’s › due to larger size of Ca 2+ than others in Ca 2 ?Mg 2+ , Fe 2+ , Mn 2+ › complete › btw Andr and Uva › due to subs. btw M1-site occupants Fe 3+ ?Cr 3+ › limited btw Gros and Uva › due to small size of Al 3+ › in T-site › P or Ti subs. for Si and Al, respectively › in hydrogarnets › SiO 2 ?2H 2 O with some vacant Si sites › Y 3+ +Al 3+ ?Mn 2+ +Si 4+ (coupled substitution in Spes)Hardness H Gar =6.5 ›7.0 Specific Gravity SG Gar =3.15 ›4.3 Colour Pyp: deep red ›black; Alm: fine deep red, brownish red; Spes: brownish ›red, pinkish; Gros: white green, yellow, cinnamon-brown (Hessonite), pale red: Andr: yellow, green (Demantoid), brown ›black (Melanite); Uva: emerald-green Streak Gar: white Luster Gar: vitreous ›resinous Tenacity Gar: brittle, friable, very tough Cleavage Absent Parting Gar: partingParting Gar: parting Fracture Gar: sub-conchoidal ›uneven Other Physical Properties Gar: cubic especially dodecahedron crystals, massive, compact, granular, transparent ›sub-translucent ALUMINOSILICATE POLYMORPHS › polymorphs › same chemical formula Andalusite (And)A l 2 SiO 5 Sillimanite (Sill)A l 2 SiO 5 Kyanite (Kya)A l 2 SiO 5 CHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES Crystal Structure and Composition › tetrahedra › independent groups › And › [ iv Al v AlO(SiO 4 )] › Al › 4- and 5-fold coordination › in orthorhombic system › Sill › [ iv Al vi Al (SiO 4 )] › Al › 4- and 6-fold coordination › in orthorhombic system › Kya › [ vi Al 2 O (SiO 4 )] › Al › Al in 6-fold coordination › in triclinic system › due to this packing of ions › SG ^ from And 70 known minerals but rare e.g. Law, Pump and Meli › also # of minerals › both TO 4 monomers and T 2 O 7 dimers e.g., Epi group and VesEPIDOTE GROUP › five important epidote group minerals Orthorhombic Epidotes Zoisite (Zoi)C a 2 (AlOH)Al 2 (SiO 4 ) 3 Monoclinic Epidotes Clinozoisite (C-Zoi)C a 2 (AlOH)Al 2 (SiO 4 ) 3 Epidote ?Pistasite (Epi) ?m Ca 2 (AlOH)Al 2 (SiO 4 ) 3 ?n Ca 2 (FeOH)Fe 2 (SiO 4 ) 3 Piedmontite (Pie)C a 2 (AlOH)(Al,Mn) 2 (SiO 4 ) 3 Allanite ?Orthite (All)( C a , F e ) 2 (AlOH)(Al,Ce,Fe) 2 (SiO 4 ) 3 CHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES Crystal Structure and Composition › silica tetrahedra › both TO 4 monomers and T 2 O 7 dimers › very complex str › (AlO,OH) 6 chains // to b-axis › linked by SiO 4 and Si 2 O 7 groups and Ca polyhedra› Zoi › minor replacement of Si by Al & Al by Fe 3+ › Mn in small quantities › C-Zoi and Epi › only limited Fe 3+ ?Al 3+ subs. › Pie › considerable variation btw Al 3+ , Fe 3+ and Mn 3+ › small quan. of Cr, Sr and Pb › All › Ca ?REE, Al ?Fe 3+ and Si ?Be subst’s › trace amounts of Nb, V, Sn, U, Th and Zn › physical properties of C-Zoi and Epi › similar Hardness H Zoi =6 ›6.5;H Epi =6 ›7;H Pie =6.5;H All =5.5 ›6 Specific Gravity SG Zoi =3.25 ›3.37;SG Epi =3.25 ›3.50;SG Pie =3.404;SG All =3 ›4.2 Colour Zoi: grayish white, gray, yellowish brown, greenish gray, apple-green, blue (Tanzanite) peach-blossom-red ›rose-red (Thulite); Epi: pistachio-green, yellowish green › brownish green, greenish black, black, red, yellow, gray, grayish white; Pie: reddish brown ›reddish black; All: brown ›blackStreak Zoi: uncoloured; Epi: uncoloured ›grayish; Pie: uncoloured ›pinkish (?) Luster Zoi: vitreous ›pearly; Epi: vitreous ›pearly ›resinous; Pie: vitreous › pearly ›resinous; All: sub-metallic ›pitchy ›resinous Tenacity Zoi: brittle; Epi: brittle; All: brittle Cleavage Zoi: very perfect; Epi: perfect; Pie: perfect; All: in traces Fracture Zoi: uneven › sub-conchoidal; Epi: uneven; Pie: uneven; All: sub-conchoidal Other Physical Properties Zoi: crystals prismatic, deeply striated, massive, columnar ›compact transparent ›sub- translucent Epi: crystals prismatic, acicular, fibrous, granular, massive, transparent ›sub- translucent ›opaque; twins are not uncommon Pie: same as Epi All: crystals tabular, long slender ›acicular prismatic, massive, zoning is common, sub- translucent ›opaqueIII. CYCLOSILICATES III. CYCLOSILICATES - characterized by rings of linked TO 4 tetrahedra - ratio of Si:O=1:3 - 3 possible closed cyclic configurations --- Si 3 O 9 , Si 4 O 12 and Si 6 O 18 rings - imp. members --- Beryl (Ber), Tourmaline (Tour), Cordierite (Cord) CHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES Crystal Structure and Composition -in beryl --- based on Si 6 O 18 --- --- Be --- in 4-fold coordination, Al in 6-fold coordination - str of Tour --- complex --- based on Si 6 O 18 --- along center of which Na + and (OH) alternate --- interlayered with rings --- sheets of triangular BO 3 groups --- (Li,Mg,Al)O 4 (OH) 2 --- octahedral groups linking Si 6 O 18 rings and BO 3 groups together --- columns of Si 6 O 18 rings --- linked to each other by (Al,Fe,Mn)O 5 (OH) groups - both --- in hexagonal systemHardness H=6.5~8 Specific Gravity SG=2. 60-3.35 Colour variable Streak Uncoloured Luster - ~resinous Tenacity Brittle Cleavage variable dependent on mineral Fracture conchoidal~uneven Other Physical Properties -Ber: prismatic habit, vertically striated, transparent ›sub-translucent - Tou: slender prismatic crystals, acicular, massive, with vertical striations // l to c-axis, transparent ›opaqueIV. INOSILICATES IV. INOSILICATES -SiO 4 tetrahedra rink into polymer-chains by sharig apical O 2- - simple single chains --- joined further sharing of O 2- in alternate tetrahedra --- double chains - in simple single chain structure --- 2 of 4 O 2- of each silica tetrahedron --- shared with a rationof Si:O=1:3 --- pyroxene group -in double polymer-chain structure --- half of tetrahedral share 3 while other half share 2 O 2- yielding a ratio of Si:O=4:11 --- amphibole groupPYROXENE GROUP - general formula --- XYZ 2 O 6 - X --- Na + , Ca 2+ , Mn 2+ , Fe 2+ and Li + - Y --- Mn 2+ , Fe 2+ , Mg 2+ , Fe 3+ , Al 3+ , Cr 3+ and Ti 4+ in the M1 site --- 6-fold regular - all coordinated of two opposing SiO 3 chains --- produce t-o-t strips - Z --- Si 4+ and Al 3+ in tetrahedral sites of chain - coordination number of the M2-site variable from 6-fold in opx to 8-fold in cpx - depending on orientation of silicate chains --- pyroxenes --- orhorhombic or monoclinic --- pyroxenoids --- triclinic system - solid solution Orthorhombic Pyroxenes (O-Pyx): Enstatite Hypersthene Ferrosilite Monoclinic Pvroxenes (CI-Pyx): Diopside Redenbergite Pigeonite Fassaite Augite Johannsenite Jadeite Omphacite Aegirine (=Acmite) Aeg-Augite Spodumene Triclinic Pvroxenoids: Wollastonite (Wol) CaSiO 3 Rhodonite Pyroxymangite Bustamite Babingtonite Diopside Diopside Hedenbergite Hedenbergite Wollastonite Wollastonite Enstatite Enstatite Ferrosilite Ferrosilite orthopyroxenes clinopyroxenes pigeoniteInosilicates: single chains- pyroxenes Diopside: CaMg [Si 2 O 6 ] a sin ß Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca)Perspective view Diopside (001) view blue = Si purple = M1 (Mg) yellow = M2 (Ca)- hardness --- 4.5 - 7 - specific gravity --- 2.96-3.8 - colour --- grayish, yellowish or greenish white, olive-green, and brown - streak --- uncoloured, grayish, brownish, white - luster --- vitreous - tenacity --- brittle - cleavage --- distinct to perfect - fracture --- uneven to sub-conchoidal AMPHIBOLE GROUP - double chains of Si 4 O 11 tetrahedra --- run // to c-axis - several cation sites - general formula --- W 0-1 X 2 Y 5 Z 8 O 22 (OH, F) 2 --- W --- Na + and K + --- in A-site (btw two chains) --- 10 ›12 coordination with O 2- and (OH) --- X --- Ca 2+ , Na + , Mn 2+ , Fe 2+ , Mg 2+ and Li + --- in M4-site --- 6 ›8 coordination --- Y --- Mn 2+ , Fe 2+ , Mg 2+ , Fe 3+ , Al 3+ and Ti 4+ --- in M1-, M2-, M3-sites --- Z --- Si 4+ and Al 3+ --- in tetrahedral sites - solid solutionTremolite Tremolite: : Ca Ca 2 2 Mg Mg 5 5 [Si [Si 8 8 O O 22 22 ] (OH) ] (OH) 2 2 Tremolite Tremolite (001) view blue = Si purple = M1 rose = M2 gray = M3 (a (001) view blue = Si purple = M1 rose = M2 gray = M3 (all Mg) ll Mg) yellow = M4 (Ca) yellow = M4 (Ca)Inosilicates: double chains- amphiboles Hornblende: Hornblende: (Ca, Na) (Ca, Na) 2 2- -3 3 (Mg, Fe, Al) (Mg, Fe, Al) 5 5 [(Si,Al) [(Si,Al) 8 8 O O 22 22 ] (OH) ] (OH) 2 2 Hornblende (001) view dark blue = Si, Al purple = M1 rose = Hornblende (001) view dark blue = Si, Al purple = M1 rose = M2 M2 light blue = M3 (all Mg, Fe) yellow ball = M4 (Ca) purpl light blue = M3 (all Mg, Fe) yellow ball = M4 (Ca) purple ball = A (Na) e ball = A (Na) little turquoise ball = H little turquoise ball = HOrthorhombic Amphiboles (O-Amp): Anthophyllite (Anth) (Mg, Fe) 7 Si 8 O 22 (OH, F) 2 Monoclinic Amphiboles (Cl-Amp) Cummingtonite (Cum) (Mg, Fe) 7 Si 8 O 22 (OH, F) 2 Grunerite (Gru) Fe 7 Si 8 O 22 (OH, F) 2 Tremolite (Tre) Ca 2 Mg 5 Si 8 O 22 (OH, F) 2 Actinolite (Act) Ca 2 (Mg, Fe) 5 Si 8 O 22 (OH, F) 2 Hornblende (Hor) (Ca, Na) 2-3 (Mg, Fe, Al)5 [Si 6 (Si,Al) 2 O 22 ] (OH,F) 2 Basaltic Hor ( ßHor) Ca 2 (Na,K) 0.5-1.0 (Mg,Fe 2+ ,Mn)) 3-2 (Fe 3+ ,Al) 2-3 Ti 0-1 [Si 6 Al 2 O 22 ] (OH, F) 2 Glaucophane (Glau) Na 2 Mg 3 Al 2 Si 8 O 22 (OH) 2 Riebeckite (Rie) Na 2 Fe 2+ 3 Fe 3+ 2 Si 8 O 22 (OH, F) 2 Arfvedsonite (Arf) Na 3 Fe 4 AlSi 8 O 22 (OH, F) 2 Tremolite Ca 2 Mg 5 Si 8 O 22 (OH) 2 Ferroactinolite Ca 2 Fe 5 Si 8 O 22 (OH) 2 Anthophyllite Mg 7 Si 8 O 22 (OH) 2 Fe 7 Si 8 O 22 (OH) 2 Actinolite Cummingtonite-grunerite Orthoamphiboles ClinoamphibolesHardness --- 5 ›6.5 Specific Gravity --- 2.85 ›3.45 Colour --- variable with composition. Streak --- uncoloured ›grayish Luster --- vitreous ›pearly ›silky Tenacity --- brittle Cleavage --- perfect prismatic Fracture --- sub-conchoidal ›unevenV. PHYLLOSILICATES=SHEET SILICATES V. PHYLLOSILICATES=SHEET SILICATES -T O 4 tetrahedra share 3 O 2- with adjacent tetrahedra --- a indefinitely extended sheet structure -T : O 2- =2:5 --- leading to T 2 O 5 - 6-fold symmetry - all of O 2- --- not shared point in the same direction --- these apical oxygen --- coordination polyhedra of cations lying btw T 2 O 5 sheets - mica-, serpentine-, clay-, and chlorite group of minerals - (OH) bearing minerals --- (OH) --- in center of 6-fold rings of tetrahedra ---at the same height as the unshared apical O 2- of the SiO 4 tetrahedra --- 2 O 2- and (OH) - --- triangles --- triangular faces of XO 6 octahedra - octahedral layer (o-layer) above [Si 2 O 5 (OH) ] 3- tetrahedral layers (t-layer) - cations in XO 6 octahedra layer --- divalent (Mg 2+ , Fe 2+ , etc.) - trioctahedral - dioctahedral •S i O 4 tetrahedra polymerized into 2-D sheets: [Si 2 O 5 ] • Apical O’s are unpolymerized and are bonded to other constituents• Tetrahedral layers are bonded to octahedral layers • (OH) pairs are located in center of T rings where no apical OMICA GROUP - more complicated than above -1 A l 3+ substituted for every 4 th Si 4+ in tetrahedral sites of Si 2 O 5 sheet - free electrical negative single charge appearing on t-o-t layer surface --- satisfied by univalent (Na + , K + ) - intelayer cations in regular 12-fold coordination - five important members: Muscovite (Mus) KAl 2 (AlSi 3 0 10 ) (OH) 2 dioctahedral Paragonite (Par)N a A l 2 (AlSi 3 0 10 ) (OH) 2 dioctahedral Phlogopite (Phl)K M g 3 (AlSi 3 0 10 ) (OH) 2 trioctahedral Biotite (Bio) K(Mg, Fe) 3 (AlSi 3 0 10 ) (OH) 2 trioctahedral Margarite (Marg)C a A l 2 (Al 2 Si 2 0 10 ) (OH) 2 dioctahedral Xanthophyllite (Xan)C a M g 3 (Al 2 Si 2 0 10 ) (OH) 2 trioctahedral Lepidolite (Lep)K ( L i , A l ) 2-3 (AlSi 3 0 10 ) (OH) 2 - little solid solution btw dioctahedral and trioctahedral groups - extensive solid solution in Phl and BioT T O O T T K K T T O O T T K K T T O O T Muscovite: K Al 2 [Si 3 AlO 10 ] (OH) 2 (coupled K - Al IV ) T-layer - diocathedral (Al 3+ ) layer - T-layer - K T K between T K between T - - O O - - T groups is stronger than T groups is stronger than vdw vdwT O T K T O T K T O T Phlogopite: K Mg 3 [Si 3 AlO 10 ] (OH) 2 T-layer - triocathedral (Mg 2+ ) layer - T-layer - K K between T - O - T groups is stronger than vdwHardness --- 2 ›4 Specific Gravity --- 2.76 ›3.3 Colour --- variable with comp. Streak --- uncoloured Luster --- vitreous ›pearly ›silky Tenacity --- cleavage flakes flexible and elastic Cleavage --- basal highly perfect Fracture --- no fracture TALC and PYROPHYLLITE GROUP - only two minerals Talc (Tal)M g 3 Si 4 O 10 (OH) 2 Minnesotaite (Min)F e 3 Si 4 O 10 (OH) 2 Pyrophyllite (Pyrp)A l 2 Si 4 O 10 (OH) 2 -T aland Pyrp --- tri-octahedral mica str. wthout interlayer cations layer --- t-o-t layers are aligned ? to c-axis --- electrically neutral --- stable structural units --- joined to eacher by van der Waals bonds - btw Tal- Min --- complete solid solution (Mg ?Fe) - Min analyses --- excess (OH) and deficiency of O 2- and low Si values --- vacant sites - Pyrp --- generally impure form --- Si ?Al and Al ?Mg, Fe 2+ , Fe 3+ , Ca, Na, K subs.Yellow = (OH) T O T - T O T - T O T vdw vdw Talc: Mg 3 [Si 4 O 10 ] (OH) 2 T-layer - triocathedral (Mg 2+ ) layer - T-layer weak van der Waals bonds between T - O - T groups Hardness H Tal =1 ›1.5; H Pryp =1 ›2 Specific Gravity SG Tal =2.7 ›2.8; SG Talc =2.65 ›2.9 Colour variable Streak Tal: white ›pale green Luster Tal: pearly; Pyrp: pearly ›glistening ›dull Tenacity Tal: sectile, thin laminæ flexible; Pyrp: laminæ flexible Cleavage Tal: basal perfect Pyrp: basal perfect Fracture Tal and Pyrp: highly cleavableCHLORITE GROUP ?ORTHOCHLORITES - closely related to micas - monoclinic system › close affinity to rhombohedral symmetry - divided into ortho- and lepto-Chl’s - Lepto-Chl’s › very complex comp. and not studied in detail - 3 imp. members in Ortho-Chl’s › hypothetical comp. combination of Tal Mg 3 Si 4 O 10 (OH) 2 + Bru 3 [Mg(OH) 2 ] layers Penninite (Pen)M g 3 Si 4 O 10 (OH) 2 3 [Mg(OH) 2 ] > MgAl 4 Si2O 10 (OH) 2 3 [Mg(OH) 2 ] Chlinochlore (Cchl)M g 3 Si 4 O 10 (OH) 2 3 [Mg(OH) 2 ] = MgAl 4 Si2O 10 (OH) 2 3 [Mg(OH) 2 ] Prochlorite (Pchl)M g 3 Si 4 O 10 (OH) 2 3 [Mg(OH) 2 ] < MgAl 4 Si2O 10 (OH) 2 3 [Mg(OH) 2 ] CHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES CHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES Crystal Structure and Composition - sheet silicate › structurally very similar to micas › except for interlayer (I) cations › additional layer of octa. Bru-like sites having (Mg,Fe,Al) 3 (OH) 6 comp. › Chl str › t-o-t building units › considerable replacement btw Mg ?Fe, Al ?Fe 3+ , Cr 3Hardness H Pen =2 ›2.5;H Cchl =2 ›2.5;H Pchl =1 ›2; H Garn =Soft (?). Specific Gravity SG Pen =2.6 ›2.85;SG Cchl =2.65 ›2.78;SG Pchl =2.78 ›2.96 ; SG Garn =2.3 ›2.8 Colour variable, mostly green Streak uncoloured ›greenish Luster pearly ›vitreous Tenacity flexible Cleavage highly perfect Fracture highly cleavableSERPENTINE GROUP - three phases › polymorphs Lizardite (Liz) Mg 3 Si 2 O 5 (OH) 4 Antigorite (Anti) Mg 3 Si 2 O 5 (OH) 4 Chrysotile (Chry) Mg 3 Si 2 O 5 (OH) 4 CHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES CHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES Crystal Structure and Composition - layered str › layer of tetrahedrally coordinated Si +4 bound into 6-membered rings + › tri-octahedral layer, Bru Mg(OH) 2 layer › layer stacking order in c-axis direction › T-O-T-O-T-O - chemistry › small replacements of Si ?Al and Mg ?Al, Fe 2+ , Fe 3+ . Ni, Cr, Cu, PtHardness H Serp =3 ›5 Specific Gravity SG Serp =2.5 ›2.65 Colour green Streak white Luster greasy Tenacity thin fibers flexible or brittle Cleavage distinct Fracture conchoidalCLAY MINERALS or CLAY GROUP 1:1 Kaolinite Group: Kaolinite (Kao)A l 2 Si 2 O 5 (OH) 4 Dickite (Dic)A l 2 Si 2 O 5 (OH) 4 Nacrite (Nac)A l 2 Si 2 O 5 (OH) 4 Halloysite (Hal)A l 2 Si 2 O 5 (OH) 4 .2H 2 O Lizardite (Liz) Mg 3 Si 2 O 5 (OH) 4 Antigorite (Anti) Mg 3 Si 2 O 5 (OH) 4 Chrysotile (Chry) Mg 3 Si 2 O 5 (OH) 4 1:2 Montmorillonite Group (Smectites): (½Ca, Na) 0.7 (Al, Mg, Fe) 4 (Si, Al) 8 O 20 (OH) 4 .nH 2 O Dioctahedral Clays I-sites O-sites T-sites Montmorillonite (Monm) (0.5 Ca Na) 0.66 Al 3.34 Mg 0.66 Si 8 Beidellite (Bei) (0.5 Ca Na) 0.66 Al 4 Si 7.34 Al 0.66 Nontronite (Non) (0.5 Ca Na) 0.66 Fe 4 +3 Si 7.34 Al 0.66 Trioctahedral Clays I-sites O-sites T-sites Saponite (Sap) (0.5 Ca Na) 0.66 Mg 6 Si 7.34 Al 0.66 Hectorite (Hec) (0.5 Ca Na) 0.66 Mg 5.34 Li 0.66 Si 8 Sauconite (Sau) (0.5 Ca Na) 0.66 Zn 4-5 (Mg,Al,Fe) 2-1 Si 6.7 Al 1.3Vermiculite (Ver) (Mg, Ca) 0.7 (Al, Mg, Fe 3+ ) 6 (Si, Al) 8 O 20 (OH) 4 .8H 2 O Sepiolite (Sep)M g 2 Si 3 O 6 (OH) 4 Illite (Ill)K 1-1.5 Al 4 [Si 7-6.5 Al 1-1.5 O 20 ] (OH) 4 Glauconite (Glac)( K , N a , C a ) 1.2-2 (Fe 3+ ,Al,Fe 2+ ,Mg) 4 [Si 7-7.6 Al 1-0.4 O 20 ](OH) 4 .nH 2 O CHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES CHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES Crystal Structure and Composition -layered str - 2 main types › 1:1 phylosilicates › T-O-T-O stacking › Kao, Dic and Nac › polymorphs › 2:1 phyllosilicates › T-O-T stacking › interlayer (I) large ions (Ca 2+ , Mg 2+ , Na + and K + surrounded by H 2 O mols) › btw T-O-T layers Hardness H= 1 ›2 Specific Gravity SG=2.3 ›2.95 Colour variableStreak colourless ›white Luster pearly ›dull earthy Tenacity flexible, inelastic, plastic Cleavage basal perfect Fracture conchoidalVI VI. . TECTO TECTOSILICATES SILICATES › highest degree of polymerization of TO4 tetrahedra › all of the O-2 in each tetrahedron › shared with adjacent tetrahedra › 3-D network › Ti:O ratio of 1:2 › TO2 general formula › Qua, Feld’s, Feldpathoids (Foid’s) and Zeolite (Zeo)SILICA MINERALS › 8 silica polymorphs (SiO 2 ) › others › amorphous or cryptocrystalline › hydrous mineraloids (Chalcedony, Opal, Allophane, and Chrysocolla) ?-Quartz ( ?-Qua)S i O 2 ß-Quartz ( ß-Qua)S i O 2 ?-Tridymite ( ?-Trid)S i O 2 ß-Tridymite ( ß-Trid)S i O 2 ?-Cristobalite ( ?-Cri)S i O 2 ß-Cristobalite ( ß-Cri)S i O 2 Coesite (Coe)S i O 2 Stishovite (Stis)S i O 2 Chalcedony (Chad)S i O 2 Opal (Opa)S i O 2 .nH 2 O Allophane (Allp)A l 2 SiO 5 .nH 2 O Chrysocolla (Chrc)C u S i O 3 .nH 2 OCHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES Crystal Structure and Composition › electrically neutral › because no other structural units › helices of …Si-O-Si-O… as in ß-Qua › silica polymorphs › stable at different P & T conditions › low P silica polymorphs › two different crystal forms › ?-forms › low T › ß-forms › high T - ß-Qua (Hex.) › ?-Qua (Tri.) - ß-Trid (Hex.) › ?-Trid (Orth) - ß-Cri (Cub.) › ?-Cri (Tet.) to more stable phases at low T. › Coe & Stis › high P polymorphs Stishovite Coesite ?- quartz ß- quartz Liquid Tridymite Cristobalite 600 1000 1400 1800 2200 2600 2 4 6 8 10 Pressure (GPa) Temperature o CLow Quartz High Quartz at 581 o C Cristobalite Stishovite Coesite ?- quartz ß- quartz Liquid Tridymite Cristobalite 600 1000 1400 1800 2200 2600 2 4 6 8 10 Pressure (GPa) Temperature o CLow Quartz Stishovite Si Si IV IV Si Si VI VI› all of the polymorphs except Stis › corner sharing 3-D tetrahedra network with Si 4+ in 4-fold tetrahedral coordination › in Stis Si 4+ › in octahedral coordination › Coe › monoclinic BUT Stis › tetragonal-system › Opa, Allp, and Chrc › amorphous › precious Opa › some degree of order within its str › comp. of Qua › nearly 100% SiO 2 -Si ?Ge, Si ?Li+Al › possible - trace amounts of Fe, Mg, Mn, Ca, Na, K and Ti › due to inclusions Hardness HQua=7;H Trid=7;H Cri=6 ›7; HCoe=7.5;H Stis=7;H Chad=7; HOpa=5.5 ›6.5;H y=3; HChrc=2.4 Specific Gravity SGQua=2.65;SG Trid=2.27;SG Cri=2.33; SGCoe=3.01;SG Stis=4.35; SGChad=2.6 ›2.64; SGOpa=1.9 ›2.3;SG Allp=1.85 ›1.89; SGChrc=2 ›2.24Colour Qua: colourless, purple or bluish violet, rose-red or pink, yellow and pelucid, smoky yellow ›dark smoky brown, black, milk white, indigo or Berlin-blue, green Trid: colourless ›white Cri: colourless ›white ›yellowish Agate-Onyx: varigated colours banded Moss Agate: irregularly clouded due to impurities Opa: play of delicate colours Opa-Agate: banded of different colours Streak white to colorless Luster Vitreous, greasy, splendent, dull, pearly, waxy, resinous Tenacity Brittle Cleavage none ›not distinct Fracture conchoidal ›sub-chonchoidal ›uneven ›splinteryOther Physical Properties Qua: variable forms › prismatic, frequently distorted crystals, massive to granular, cryptocrystalline, mammillary, stalagtitic, concretionary forms, piezo-electric and pyro- electric property, transparent ›translucent › opaque Trid: minute crystals, in fan-shaped groups, transparent Opal: amorphous, colloidal, massive, reniform, stalagtitic, earthy transparent ›opaqueFELDSPAR GROUP › general formula › AT 4 O 8 , -T -sit es › Si +4 , Al +3 , occasionally Fe +3 -A-sit e › Na + , K + , Ca +2 , rarely Ba +2 , Sr +2 Monoclinic Feldspars Sanidine (San) KAlSi 3 O 8 Orthoclase (Ort) KAlSi 3 O 8 A-Feldspar (A-Feld) (K, Na)AlSi 3 O 8 Hyalophane (Hya) (K 2 , Ba)Al 2 Si 4 O 12 Celsian (Cels) BaAl 2 Si 2 O 8 Triclinic Feldspars Microcline (Mic) KAlSi 3 O 8 Anorthoclase (Aort) (Na, K)AlSi 3 O 8 Plagioclase Series (Pla) n NaAlSi 3 O 8 (Alb), m. Ca Al 2 Si 2 O 8 (Ano) Albite (Alb) Alb 100-90 Ano 0-10 Oligoclase (Olig) Alb9 0-70 Ano 10-30 Andesine (Ande) Alb 70-50 Ano 30-50 Labradorite (Lab) Alb 50-30 Ano 50-70 Bytownite (Byt) Alb 30-10 Ano 70-90 Anorthite (Aort) Alb 10-0 Ano 90-100CHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES Crystal Structure and Composition › general formula › AT 4 O 8 › T-site › tetrahedral 4-fold coordination site › Si +4 , Al +3 and occasionally Fe +3 . › A-site › large irregular cavity with a C.N of about 9 › Na + , K + , Ca +2 , rarely Ba +2 and Sr +2 › general architecture of the Feld structure › best illustrated by studying high-San polymorph (monoclinic system) › Al-Si distribution › completely disordered › Al and Si ions › randomly distributed among distinc tetrahedral sites T1 and T2 › K+ ions › bonded to 9 nearest O 2- in a large interstices (A-sites) › Si-Al tetrahedral framework › 4 membered rings of tetrahedra › linked into chainsAlbite: NaAlSi 3 O 8› Feld’s › two major series based on A-site occupancy › A-Feld series › from Alb NaAlSi 3 O 8 to ‘Ort’ KAlSi 3 O 8 K-Feld › 3 main polymorphs › San, Ort and Mic › Pla series › from Alb NaAlSi 3 O 8 to Ano CaAl 2 Si 2 O 8 › significant miscibility gap between Pla Feld’s and A-Feld › due to large difference between K + ?Ca +2 ions during substitution › only allowed at very high T › A-Feld › Na + ?K + › significant › at LT › exsolution › Pla series › coupled substitution of Na + +Si +4 ?Ca 2+ +Al +3› in A-Feld group › complete solid solution at HT › high-San (Mono), low-b (Mono); Ort (Mono), Mic (Tric), Aort (Tric), high-Alb (Tric), low-Alb (Tric) › at LT › miscibility gap › perthitic or antiperthitic A-felds › in Plag group › complete solid solution btw Alb-Ano › Olig (An 10-30 ) Ande (An 30-50 ) Lab(An 50-70 ) and Byt (An 70-90 ) › triclinic system › other ions present › in A-Feld str › Ba, Ti, Fe 3+ , Fe 2+ , Mg, Sr, rarely Mn › in Pla series › Li, Ti, Fe 3+ , Fe 2+ , Mn, Mg, Ba, and SrHardness H=6-6.5 Specific Gravity SG=2.56 ›3.37 Colour San: colourless Ort: colourless, white, gray, flesh-red, pale yellow, green Mic: white ›pale cream-yellow, red, green Aort: same as other A-Feld’s Alb: white, bluish, gray, reddish, greenish, green, bluish opalescence/ play of colours Pla: colourless, white, gray, greenish, yellowish, flesh-red Ano: white, grayish, reddish Streak white to uncoloured Luster vitreous, pearly Tenacity brittleCleavage perfect › good Fracture chonchoidal › uneven Other Physical Properties San: tabular crystals, twinning common, transparent ›glassy Ort: short prismatic crystals, frequently twinned, coarse cleavable ›granular masses, fine-grained massive, formless grains, transparent variety Alb: tabular crystals commonly twinned, massive, granular (fine ›impapable) or laminar, laminæ often curved and divergent, transparent ›sub-translucent Pla: tabular and elongated crystal, frequently twinned, striations on basal cleavage, cleavable masses, as irregular grains, compact, transparent ›sub-translucentZEOLITE GROUP › large group of hydrous silicates › close similarities in composition, association, and mode of occurrence to Feld’s › framework aluminosilicates with Na, Ca, and K, and highly variable amounts of H2O in generally large voids of framework Tetragonal Zeolite-like Sheet Silicate Apophyllite (Apo) Ca 4 (Si 2 O 5 ) 4 . KF.8H 2 O Hexagonal Zeolites Chabazite (Chab) Ca 2 Al 2 Si 4 O 12 .6H 2 O Orthorhombic Zeolites Natrolite (Nat) Na 2 Al 2 Si 3 O 10 .2H 2 O Thomsonite (Tho) (Ca, Na 2 ) 2 Al 4 Si 4 O 16 .5H 2 O Monoclinic Zeolites Stilbite (Stil) NaCa 2 Al 5 Si 13 O 36 .14H 2 O Laumontite (Lau) (Ca, Na 2 )Al 2 Si 4 O 12 .4H 2 O Heulandite (Heu) CaAl 2 Si 7 O 18 .6H 2 O Philipsite (Phi) (K 2 , Ca) 2 Al 4 Si 8 O 24 .9H 2 OCHARACTERISTIC PHYSICAL and CHEMICAL PROPERTIES Crystal Structure and Composition › spacious channels › H 2 O molecules, variable amounts of Na, Ca, K that › housed in the channels and framework atoms › Apo › Si 2 O 5 sheets › 4-fold and 8-fold rings › linked to each other with hydrated Ca, K + and F - ions › Chab › Al-Si-O framework with large openings bonded by rings of tetrahedral › connected to each other with large channels › Nat › Al-Si-O framework in which chains //l to the c-axis › chains linked laterally by sharing of some O 2- of opposing tetrahedral › Na › coordinated btw chains to 6 O 2- › 4 of which tetrahedral O 2- and 2 of which › from H 2 O molecules Hardness H=3.5 ›5.5 Specific Gravity SG=2.05 ›3.52 Colour colourless, white, grayish, pale shades of green, yellow, rose-red, flesh-red, yellow, pink, red, grayStreak uncloured Luster. vitreous ›pearly Tenacity Brittle Cleavage highly perfect to poor depending on variety Fracture mostly uneven, sub-conchoidal Other Physical Properties massive, lamellar, concentric, radiated, prismatic crystals, rhombohedral crystals, acicular, fibreous, columnar, transparent ›translucent