GY 302 Mineralogy Lab 11 Silicates Nesosilicates Isolated

GY 302 Mineralogy Lab 11: Silicates

Nesosilicates (Isolated Si. O 4 tetrahedra)

Nesosilicate Minerals • Olivine Group – – – • • • Fayalite (Fe 2 Si. O 4); Forsterite (Mg 2 Si. O 4) Olivine has complete solid solution between Fayalite and Forsterite. Crystal: Orthorhombic Pt. Group: 2/m 2/m Habit: prismatic, granular S. G. : 3. 2; H: 6. 5 L: vitreous; Str: white Col: colorless-green (For) yellow (Fay) Clev: {010} indistinct Optics: Biaxial +/nα= 1. 651; nβ= 1. 670; nγ= 1. 689 Diagnostic: color and granular nature. Occurrence: mainly in mafic and ultramafic igneous rocks; also in marbles and skarns. Olivine is a significant component of the Earth’s mantle, therefore, it is one of the most common silicates in the interior Earth even though being somewhat rare in continental crust. Olivine is typically a major proportion of stony meteorites. Forsterite (named after Johann Forster, German naturalist ). . Fayalite (named after the Fayal Island, Azores)

Nesosilicates: Garnet Group • • Pyrope (Mg 3 Al 2(Si. O 4)3) Almandine (Fe 3 Al 2(Si. O 4)3) Grossular (Ca 3 Al 2(Si. O 4)3) Spessartine (Mn 3 Al 2(Si. O 4)3) – • • • Complete solid solution exists between all of the 4 end member components. Crystal: Isometric Pt. Group: 4/m 3 2/m Habit: dodecahedral SG: 3. 54 -4. 33; H: 6. 5 -7. 5 L: vitreous/resinous. Col: variable. Clev: none, parting on {110} Optics: Isotropic (n=1. 544) Diagnostic: crystal form, lack of cleavage, hardness are diagnostic. Occurrence: widely distributed in Al-rich metamorphic rocks; also in skarns. Almandine

Garnet • • • Occurrence: Middle to high-grade metamorphic rocks, placer deposits Associated Minerals: mica minerals, staurolite, medium to high-grade metamorphic minerals, rarely diamonds Can be confused with: when crystalline, nothing, but distinguishing garnet varieties is problematic without a chemical analysis. Uses: abrasive, sand blasting, gemstones Sandpaper, Emory board). Ultra-high pressure metamorphic rocks named Eclogite are garnet-bearing peridotites. Grossular

Aluminosilicates • • • • Aluminum Silicates polymorphs: Kyanite (Al 2 Si. O 5) Andalusite (Al 2 Si. O 5) Sillimanite (Al 2 Si. O 5) Crystal: Triclinic Pt. Group: 1 Habit: Fibrous (Sill. ), bladed (Ky. ), and prismatic (And. ) SG: 3. 61; H: 4 -7 varies with crystal axes. L: vitreous, pearly. Streak: white. Color: blue - white (blue, pink, grey) Cleavage: [100] perfect, [010] imperfect Optics: Biaxial - nα= 1. 712; nβ= 1. 720; nγ= 1. 728 Diagnostic: bladed habit and color are usually diagnostic. Variable hardness is unique. Occurrence: kyanite is widely distributed in Al-rich regional metamorphic rocks of Barrovian metamorphic facies. The aluminosilicate stability fields are well-known so this mineral may be critical for determining the P-T conditions of recrystallization. Optically kyanite has an unusual blue pleochroism. Kyanite: from the Greek kyanos for blue.

Andalusite • • • Crystal: Orthorhombic Pt. Group: 2/m 2/m Habit: prismatic (w crosses) SG: 3. 15; H: 7. 5* (warning!) L: vitreous; Str: white Col: white, red, brown, grey Clev: [110] fair, [100], [010] poor Optics: Biaxial - nα= 1. 629; nβ= 1. 633; nγ= 1. 639 Diagnostic: crystal habit and mode of occurrence in low -P regional metamorphic rocks. Occurrence: restricted to contact metamorphic or regional Buchan facies Al-rich rocks. Named after Andalucia, Spain. Chiastolite variety

Sphene (Titanite) Ca. Ti. Si. O 5 • • • Crystal: Orthorhombic Pt. Group: 2/m 2/m Habit: massive, bladed S. G. : 3. 48 Hardness: 5 -5. 5 Luster: adamantine-resinous Streak: reddish-white Color: reddish brown (grey, green, yellow) Cleavage: [110], [100], [112] poor Optics: Biaxial + nα= 1. 887; nβ= 1. 894; nγ= 1. 979 Diagnostic: Color, wedge or diamond shaped cross-sections, adamantine luster. Occurrence: widely distributed as an accessory mineral in felsic to intermediate igneous rocks. Very common in calc-silicate gneisses and skarns. Titanite: named for its titanium content.

Staurolite • • • Crystal: Monoclinic Pt. Group: 2/m Habit: crystals common; prismatic {001}, {010} ; twins common producing the famous “cross”. S. G. : 3. 7 – 3. 8. Hardness: 7. 0. Luster: adamantine-resinous Streak: reddish-white Color: brown. Streak is grey. Cleavage: {010} distinct. Optics: Biaxial + nα= 1. 736; nβ= 1. 740; nγ= 1. 745. Diagnostic: color and habit. Occurrence: widely distributed in Al-rich mid- to high-grade regional metamorphic rocks. Note that staurolite is a hydrated silicate and will be lost to high-grade granulite facies dehydration reactions. By Rob Lavinsky, i. Rocks. com – CC-BY-SA-3. 0, CC BY-SA 3. 0, https: //commons. wikimedia. org/w/index. php? curid=101223 63.

Sorosilicate Formulas • • • Lawsonite: Ca. Al 2 Si 2 O 7(OH)2 IH 2 O Pumpellyite: Ca 2 Mg. Al 2(Si. O 4)(Si 2 O 7)(OH)2 IH 2 O Vesuvianite: Ca 10 Mg 2 Al 4(Si. O 4)5(Si 2 O 7)2(OH)2 Zoisite: Ca 2 Al 3 Si 3 O 12(OH) Clinozoisite: Ca 2 Al 3 Si 3 O 12(OH) Epidote: Ca 2(Al, Fe)3 Si 3 O 12(OH)

Sorosilicates (2 linked Si. O 4 Tetrahedra) • One corner of 2 linked Si. O 4 tetrahedra are shared. • Sharing one corner results in a Si: O ratio in the mineral formula of 2: 7. • Structures of Si 2 O 7 tetrahedral pairs are bonded to other cations such as Ca and Al. • Structures with Si 2 O 7 pairs and unlinked Si. O 4 are also possible.

Lawsonite: Ca. Al 2 Si 2 O 7(OH)2*H 2 O • • • Crystal: Orthorhombic Pt. Group: 2/m 2/m Habit: crystals uncommon; prismatic. S. G. : 3. 09. Hardness: 8. 0. Luster: vitreous to greasy. Transparent to translucent. Color: white, pale blue, pale gray. Cleavage: {100}, {001} perfect. {110} indistinct. Optics: Biaxial + nα= 1. 665; nβ= 1. 672 -1. 676; nγ= 1. 684 -1. 686. Diagnostic: hardness and high S. G. , association with glaucophane. Occurrence: found in blueschist facies glaucophane schists.

Pumpellyite: Ca 2 Mg. Al 2(Si. O 4)(Si 2 O 7)(OH)2 IH 2 O Crystal: Monoclinic Pt. Group: 2/m Habit: acicular, bladed, or fiberous. S. G. : 3. 18 -3. 23. Hardness: 5. 5 -6. Luster: vitreous to translucent. Color: green to brown. Cleavage: {001} distinct. {100} less distinct. • Optics: Biaxial + nα= 1. 674 -1. 748; nβ= 1. 675 -1. 754; nγ= 1. 688 -1. 764. • Diagnostic: resembles epidote but has deeper colors. • Occurrence: occurs in zeolite and blueschist facies metamorphic rocks. • •

Vesuvianite (Idocrase): Ca 10 Mg 2 Al 4(Si. O 4)5(Si 2 O 7)2(OH)2 • Crystal: Tetragonal • Pt. Group: 4/m 2/m • Habit: crystals common, prismatic or pyramidal, also massive. • S. G. : 3. 3 -3. 6. • Hardness: 7. 0. • Luster: vitreous to resinous. • Color: typically brown or green; in some cases yellow or blue. • Cleavage: {110} indistinct. • Optics: uniaxial – W=1. 702 -1. 752; E= 1. 6981. 746. • Diagnostic: resembles garnet in massive variety; crystal form and hardness. • Occurrence: occurs in contact metamorphic skarns and other metamorphic Ca-silicate rich compositions.

Zoisite: Ca 2 Al 3 Si 3 O 12(OH) • • • Crystal: Orthorhombic Pt. Group: 2/m 2/m Habit: single crystals uncommon; aggregates of long prismatic crystals. S. G. : 3. 3. Hardness: 6. 5. Luster: vitreous to pearly. Transparent to translucent. Color: typically gray; some cases pink, applegreen, blue, or purple. Cleavage: {001} perfect. Optics: biaxial – nα= 1. 685 -1. 707; nβ= 1. 6881. 711; nγ= 1. 697 -1. 725. Diagnostic: distinguished from amphiboles that it resembles by one direction of perfect cleavage. Occurrence: occurs in schists and gneisses, and as an alteration product of plagioclase.

Clinozoisite, Epidote: Ca 2 Al 3 Si 3 O 12(OH) • • • Crystal: Monoclinic Pt. Group: 2/m Habit: crystals common, elongated parallel to b axis; also massive. S. G. : 3. 3 -3. 6. Hardness: 7. 0. Luster: Vitreous. Transparent to translucent. Color: pale green to green-gray for clinozoisite; yellowish to brown-green for Epidote. Cleavage: {001} perfect. Optics: biaxial – nα= 1. 703 -1. 715; nβ= 1. 7071. 725; nγ= 1. 709 -1. 734. Diagnostic: hardness and yellow-green color. Occurrence: low- to medium grade regional metamorphic rocks, usually as the principle Ca-Al silicate.

Cyclosilicates (Si. O 4 Ring composed of 6 Si. O 4 Tetrahedra) • 2 corners of each Si. O 4 tetrahedron is shared with a neighbor resulting in a 1: 3 ratio. • Crystallography tends to be hexagonal, Trigonal, or pseudohexagonal. • The ring structure allows for unusually large ions to fit inside the ring structure (Li, Cs, Be, K). For this reason cyclosilicates are often termed “Garbage Can Minerals”.

Tourmaline [WX 3 Y 6(BO 3)3(Si 6 O 18)(OH, F)4] W=(Ca, Na, K); X=(Al, Fe, Li, Mg, Mn); Y=(Al, Cr, Fe, V) • • • Crystal: Trigonal Pt. Group: 3 m Habit: crystals common; typically prismatic crystals with rounded triangular cross-section. S. G. : 3. 0 -3. 2. Hardness: 7. 5. Luster: Vitreous. Transparent to Translucent. Streak: white. Color: black, brown, dark blue, pink, green, colorless. Cleavage: {1120}, {1011} indistinct. Diagnostic: color, triangular crosssection, striations on prism faces. Occurrence: mainly in granite pegmatites and adjacent country rock. By JJ Harrison (https: //www. jjharrison. com. au/) - Own work, CC BY-SA 3. 0, https: //commons. wikimedia. org/w/index. php? curid=7515672. Name Source: name comes from the word "thoramalli" (ත රමලල ) or "tōra- molli", which is applied to a group of gemstones found in the southern parts of the Indian Subcontinent.

Beryl (Be 3 Al 2 Si 6 O 18) • Crystal: Hexagonal • Pt. Group: 6/m 2/m • Habit: prismatic hexagonal crystals common. • S. G. : 2. 65 -2. 95. • Hardness: 8. 0. • Luster: Vitreous. Transparent to Translucent. • Color: violent to brown, yellow, green-yellow or pink. white. • Cleavage: {0001} distinct. • Diagnostic: crystal form and hardness are diagnostic. Apatite is similar but hardness is much lower (5). • Occurrence: mainly in granite pegmatites and adjacent country rock. •

Cordierite: Al 3(Mg, Fe)2(Si 5 Al. O 18) • • • Crystal: Orthorhombic Pt. Group: 2/m 2/m Habit: crystals uncommon. Most are prismatic. S. G. : 2. 55 -2. 75 l Hardness: 7. 0. Luster: Vitreous. Transparent. Color: colorless, blue, violet, gray, yellow, brown. Cleavage: {0001} distinct. Diagnostic: blue to blue-gray color, when colorless it is very similar to quartz. Occurrence: mainly in medium to high-grade metamorphic rocks, however, is typically found in terranes with a higher than normal Barrovian geothermal gradient. Also found in contact metamorphic rocks. .

Inosilicate Formula’s

Inosilicate (Chain and Double Chain) Structure • Single chain: two corners of each Si. O 4 tetrahedron are shared in a linear chain. • This results in a Si: O ratio of 1: 3. • Double chain: alternating 2 - and 3 - corners of Si. O 4 tetrahedra are shared to form a linear double-chain structure. • This results in a Si: O ratio of 4: 11.

Enstatite, Hyperthene [(Mg, Fe)Si. O 3] • • • Crystal: Orthorhombic (Orthopyroxene=opx) Pt. Group: 2/m 2/m Habit: crystals uncommon; typically cleavable masses. S. G. : 3. 18 -3. 9 Hardness: 6. 0. Luster: Vitreous. Translucent. Streak: White to gray. Color: pale green, brown-green, brown, black, bronze. Cleavage: {210} good; cleavage planes at approximately 90 degrees Diagnostic: pyroxene cleavage, crystal form, and color distinguish opx from cpx. Occurrence: a major constituent of mafic and ultramafic igneous rocks. Also occurs in granulite facies regional metamorphic rocks and eclogites. CC BY 2. 0, https: //commons. wikimedia. org/w/index. php? curid=16 4237.

Diopside, Hedenbergite [Ca(Mg, Fe)Si 2 O 6] • • • Crystal: Monoclinic (Clinopyroxene=cpx) Pt. Group: 2/m Habit: crystals common; typically short, prismatic with square cross-sections. S. G. : 3. 25 -3. 55. Hardness: 6. 0. Luster: Vitreous. Translucent. Streak: White to gray. Color: dark green to black. Cleavage: {110} good; cleavage planes at approximately 90 degrees. Diagnostic: crystal form, cleavage, and color are diagnostic. Occurrence: a major constituent of mafic and ultramafic igneous rocks; also in skarns. By Didier Descouens - Own work, CC BY-SA 3. 0, https: //commons. wikimedia. org/w/index. php? curid=14047390.

Hornblende [(Ca, Na, K)2 -3(Mg, Fe, Al)5 Si 6(Si, Al)2 O 22(OH, F)2] • • • Crystal: Monoclinic Pt. Group: 2/m Habit: crystals common; prismatic with hexagonal cross-sections. S. G. : 3. 0 -3. 4. Hardness: 6. 0. Luster: Vitreous. Translucent. Streak: Gray or pale green. Color: Dark green, black. Cleavage: {110} perfect; 2 directions at 120 and 60 degrees. Diagnostic: color, crystal form, cleavage. Darker than other amphiboles. Occurrence: Widely distributed in intermediate and felsic igneous rocks. Also in regional metamorphic rocks, especially amphibolites. By Rob Lavinsky, i. Rocks. com – CC-BY-SA-3. 0, CC BY-SA 3. 0, https: //commons. wikimedia. org/w/index. php? curid=10 175167. Name Origin: derived from the German horn and blenden, to 'deceive' in allusion to its similarity in appearance to metal-bearing ore minerals.

Glaucophane [Na 2 Mg 3 Al 2 Si 8 O 22(OH)2] • • • Crystal: Monoclinic Pt. Group: 2/m Habit: crystals uncommon; prismatic to acicular; fiberous; aggregates of small grains. S. G. : 3. 0 -3. 4. Hardness: 6. 0. Luster: Vitreous. Translucent. Streak: White to blue-gray. Color: pale blue, lavender blue. Cleavage: {110} perfect; 2 directions at 120 and 60 degrees. Diagnostic: similar to other amphiboles except for blue color. Occurrence: a major constituent of blueschist facies Al-rich rocks. By Didier Descouens - Own work, CC BY-SA 4. 0, https: //commons. wikimedia. org/w/index. php? curid=14812103. Name Origin: Glaucophane is named for its typical blue color. In Greek, glaucophane means "blue appearing".

Phyllosilicate Formula’s

Phyllosilicate Structure (Sheet) • In phyllosilicates 3 corners of each Si. O 4 tetrahedron is shared to form a 2 -dimensional sheet. The other cations in the formula weakly bond these sheets together. • This structure results in a Si: O ratio of 4: 10. Al and Fe can substitute for Si to a limited extent.

Muscovite [KAl 3 Si 3 O 10(OH)2] • • • Crystal: Monoclinic Pt. Group: 2/m Habit: crystals common; tabular with pseudo-hexagonal sheets. S. G. : 2. 8 -2. 9. Hardness: 2. 0 on cleavage. Luster: Vitreous. Transparent. Streak: White. Color: colorless to pale green, gray, brown. Cleavage: {001} perfect. Elastic sheets. Diagnostic: cleavage, elastic sheets, color. Occurrence: a common accessory mineral in intermediate and felsic igneous rocks. A major component of Al-rich intermediate and high-grade regional metamorphic rocks. By Rob Lavinsky, i. Rocks. com – CC-BY-SA-3. 0, CC BY-SA 3. 0, https: //commons. wikimedia. org/w/index. php? curid=10149941. Name origin: name muscovite comes from Muscovy-glass, a name given to the mineral in Elizabethan England due to its use in medieval Russia as a cheaper alternative to glass in windows.

Biotite [K(Mg, Fe)3 Al. Si 3 O 10(OH)2] • • • Crystal: Monoclinic Pt. Group: 2/m Habit: crystals common; tabular with pseudo-hexagonal sheets. S. G. : 2. 8 -3. 4. Hardness: 2. 5 on cleavage. Luster: Vitreous. Transparent to translucent. Streak: White or gray. Color: dark green, brown, black. Cleavage: {001} perfect. Elastic sheets. Diagnostic: cleavage, elastic sheets, color. Occurrence: an common accessory mineral in mafic to felsic igneous rocks; a major component of intermediate to high -grade regional metamorphic rocks. By James St. John - Biotite mica 2, CC BY 2. 0, https: //commons. wikimedia. org/w/index. php? curid=76867216. Name origin: named by J. F. L. Hausmann in 1847 in honor of the French physicist Jean-Baptiste Biot, who performed early research into the many optical properties of mica. .

Tectosilicate Formula’s Mineral Formula System Quartz Si. O 2 Trigonal Sanadine KAl. Si 3 O 8 Monoclinic Orthoclase KAl. Si 3 O 8 Monoclinic Microcline KAl. Si 3 O 8 Triclinic Amazonite KAl. Si 3 O 8 Triclinic Albite Na. Al. Si 3 O 8 Triclinic Anorthite Ca. Al 2 Si 2 O 8 Triclinic Anorthoclase (Na, K)Al. Si 3 O 8 Triclinic Plagioclase Composition: Oligoclase (An 10 -30) Andesine (An 30 -50) Labradorite (An 50 -70) Bytownite (An 70 -90)

Tectosilicate (Framework) Structure • In tectosilicates all 4 corners of every Si. O 4 tetrahedron is shared producing a 3 D framework. • This results in a Si: O ratio of 1: 2. • In many tectosilicates Al will substitute for Si in some of the tetrahedrons (i. e. forming Al. O 4 tetrahedrons). • The other cations fit between the tetrahedrons in 12 coordination with O.

Quartz (Si. O 2) • • • • Crystal: Hexagonal (Trigonal) Pt. Group: 32 Habit: bipyramidal, massive, drusy etc. SG: 2. 65; H: 7 L: vitreous Str: colorless Col: colorless (varied) Cleav: fracture conchoidal. Optics: Uniaxial (-); bir=0. 009 nw=1. 544; ne=1. 553 Occurrence: widespread Diagnostic: H, fracture, crystal habit, striated prism faces. Occurrence: a mjor component of felsic to intermediate igneous rocks. Also a major component of silica-rich sedimentary and metamorphic rocks. Name Derivation: From the German “quarz” of uncertain origin.

Orthoclase (KAl. Si 3 O 8) • • • • Crystal: Monoclinic Pt. Group: 2/m Habit: prismatic, blocky SG: 2. 56; H: 6 L: vitreous Str: colorless Col: pink, white, grey-green Clev: perfect [001], good [010] Optics: biaxial (-); bir=0. 005 -0. 006 Nα=1. 518; nβ=1. 522, nγ=1. 523 Occurrence: widespread in continental crustal rocks. Diagnostic: cleavage, habit, color, H. Occurrence: a major component of the continental crust, common in all quartzofeldspathic igneous, sedimentary, and metamorphic rocks http: //webmineral. com Name origin: From the Greek orthos - "right" and kalo -" I cleave“.

Microcline, Amazonite (KAl. Si 3 O 8) Crystal: Triclinic Pt. Group: 1 Habit: prismatic, blocky SG: 2. 56; H: 6 L: vitreous/pearly; Str: colourless Col: bluish-green, white, grey Clev: perfect [001], good [010] Optics: biaxial (-); bir=0. 007 nα=1. 518; nβ=1. 522, nγ=1. 525 Diagnostic: color, crystal form, cleavage. • Occurrence: a common constituent of felsic igneous rocks. • • •

Albite (Clevelandite) [Na. Al. Si 3 O 8] • • • Crystal: Triclinic Pt. Group: 1 Habit: prismatic, blocky SG: 2. 62 H: 6 L: vitreous Streak: colorless Col: white (greyish, greenish, bluish) Cleavage: perfect [001], good [010] Optics: biaxial (-); bir=0. 007 nα=1. 518; nβ=1. 522, nγ=1. 523 Occurrence: granite pegmatities etc. Diagnostic: crystal form, H, cleavage, striattions on {010}, light color. Name origin: From the Latin, albus, in allusion to the common color.

Labradorite (Spectrolite) [An 50 -70] Crystal: Triclinic Pt. Group: 1 Habit: granular, blocky striated SG: 2. 69 H: 6 L: vitreous Str: colourless Col: colorless, grey (iridescent) Cleav. : perfect [001], good [010] Optics: biaxial (+); bir=0. 009 -0. 010 nα=1. 554; nβ=1. 559, nγ=1. 562 • Occurrence: Mafic igneous rocks, some metamorphic rocks. • Diagnostic: cleavage, H, striations on {010}, iridescent colors. • • •

Feldspathoid Group Mineral Formula System Leucite KAl. Si 2 O 6 Tetragonal Nepheline Na. Al. Si. O 4 Hexagonal Sodalite Na 8(Al. Si. O 4)6 Cl 2 Isometric Lazurite (Na, Ca)8(Al. Si. O 4)6(SO 4, S, Cl)2 Isometric

Sodalite [Na 8 Al 6 Si 6 O 24 Cl 12] • • • Crystal: Isometric Pt. Group: 43 m Habit: massive, vein-fill SG: 2. 29 H: 6 L: vitreous-greasy Str: white Col: azure blue, white, pink, grey Clev: poor [110] Optics: isotropic; n=1. 4831. 484 Occurrence: Nepheline syenites Diagnostic: blue color, H, translucent.