UNIVERSITY OF SOUTH ALABAMA GY 302: Crystallography & Mineralogy Lecture 21: Inosilicates 1 Pyroxenes and Pyroxenoids Last Time Class VIII Minerals 1. Sorosilicates 2. Cyclosilicates (3, 4 and 6 fold coordination) Sorosilicates Mineral Formula System Zoisite Ca2Al3O(SiO4)(Si2O7)(OH) Orthorhombic Clinozoisite Ca2Al3O(SiO4)(Si2O7)(OH) Monoclinic Epidote Ca2(Al,Fe)Al2O(SiO4)(Si2O7)(OH) Monoclinic Allanite (Ca,Ce) 2(Fe,Fe)Al2O(SiO4)(Si2O7)(OH) Monoclinic Lawsonite CaAl2SiO7(OH)2·H2O Orthorhombic Pumpellyite Ca2MgAl2(SiO4)(Si2O7)(OH)2·H2O Monoclinic Vesuvianite (Idocrase) Ca10Mg2Al4(SiO4)5(Si2O7)2(OH)4 Tetragonal Hemimorphite Zn4Si2O7(OH)2·(H2O) Orthorhombic Sorosilicate Minerals Hemimorphite [Zn4Si2O7(OH)2·H2O] Crystal: Orthorhombic Pt. Group: 2mm Habit: massive to mammillary SG: 3.45; H: 5 L: vitreous; Str: white Col: colorless, brown, to grey Clev: perfect [001] Optics: Biaxial (+); bir=0.020 nα=1.61; nβ=1.62, nγ=1.736 http://webmineral.com/data/Hemimorphite.shtml Named after the hemimorphic nature of the crystals. Cyclosilicates Mineral Formula System Beryl Be3Al2Si6O18 Hexagonal “Tourmaline” (Na,Ca)(Li,Mg,Al)(Al,Fe,Mn) 6(BO3)3(Si6O18)(OH)4 Hexagonal (Trigonal) Cordierite Al3(Mg, Fe)2(AlSi5O18) Orthorhombic Axinite (Ca, Mn, Fe)3Al2(BO3)Si4O12(OH) Triclinic Dioptase CuSiO2(OH)2 Hexagonal (Trigonal) Silicate rings come in 3, 4 and 6 fold structures. 8-fold structures also occur in nature (e.g., sulfur) Cyclosilicate Minerals 6 fold ring structure Cyclosilicate Minerals (6-fold rings) Beryl [Be3Al2Si6O18 ] Crystal: Hexagonal Pt. Group: 6/m 2/m 2/m Habit: euhedral, columnar SG: 2.76; H: 7.5-8 L: vitreous; Str: white Col: blue, yellow, red, green Clev: imperfect Optics: Uniaxial (-); bir=0.004-0.007 ne=1.564; nw=1.568 http://webmineral.com/specimens/picshow.php?id=123 From the ancient Greek, beryllos, signifying a "precious blue-green color of sea water" stone. Today’s Agenda Class VIII Minerals: Inosilicates (part 1) 1. General Introduction to Inosilicates 2. Pyroxenes 3. Pyroxenoids Inosilicates The “chain” silicates come in 2 main “flavors” Single chains (Si:O = 1:3) (Pyroxene Group) (Pyroxenoid Group) Double chains (Si:O = 1:2.5) (Amphibole Group) Inosilicates (single chain) Two major sub groups of pyroxenes are distinguished on the basis of crystal structure: 1) Orthopyroxenes (orthorhombic) 2) Clinopyroxenes (monoclinic) http://www.uwgb.edu/dutchs/GRAPHIC0/ROCKMIN/ATOM-STRUCT/PyroxChain.gif Inosilicates (single chain: pyroxenes) General formula: XYSiO3 or XY(Si,Al)2O6 X[larger ions] = Ca2+, Na+, Fe2+ and/or Mg2+; rarely Zn2+, Mn2+, Li+ Y[smaller ions] = Cr3+, Al3+, Fe3+, Mn3+ Si:O ratio is 1:3 (octahedrally coordinated cations between SiO3 chains) http://www.tulane.edu/~sanelson/images/opx-cpxphasediag.gif Inosilicates (single chain: pyroxenes) General formula: XYSiO3 or XY(Si,Al)2O6 X[larger ions] = Ca2+, Na+, Fe2+ and/or Mg2+; rarely Zn2+, Mn2+, Li+ Y[smaller ions] = Cr3+, Al3+, Fe3+, Mn3+ Monoclinic Orthorhombic Si:O ratio is 1:3 (octahedrally coordinated cations between SiO3 chains produce orthorhombic or monoclinic symmetries) http://ruby.colorado.edu Inosilicates (single chain; pyroxenoids) General formula: X2SiO3 X[larger ions] = Ca2+, Na+, Fe2+ and/or Mg2+ Si:O ratio is 1:3 (larger cations force triclinic symmetry) http://ruby.colorado.edu Inosilicates (single chain) Orthopyroxene: orthorhombic minerals (5) Hypersthene, Enstatite, Ferrosilite, Donpeacorite, Nchwaningite Clinopyroxene: monoclinic minerals (18) Clinoenstitite, clinoferrosilite, pigeonite, diopside, hedenbergite, spudomene Pyroxenoid: Triclinic minerals (lots) wollanstonite, pectolite, rhodonite Inosilicates (single chain) Inosilicate Minerals (orthopyroxene) Enstitite [Mg2Si2O6] Crystal: Orthorhombic Pt. Group: 2/m 2/m 2/m Habit: laminar, massive, fibrous SG: 3.2; H: 5.5 L: vitreous to pearly; Str: grey Col: white, yellow, brown, gray Clev: [110]; [010] good Optics: Biaxial (+); bir=0.009 nα=1.65; nβ=1.65, nγ=1.66 Occurrence: mafic intrusive rocks From the Greek enstates - "opponent." Inosilicate Minerals (orthopyroxene) Enstitite is actually one member of a continuous series suite of “orthopyroxene” (Enstitite-Ferrosilite). 2009 textbook’s “mineral” (p265) Orthopyroxenes hyperstene http://ruby.colorado.edu/~smyth/min/images/enstatite.gif http://upload.wikimedia.org/wikipedia/en/4/42/Pyrox_names.png Inosilicate Minerals (orthopyroxene) Enstitite (En) can also be related to many other silicate minerals through this phase diagram http://www.geo2all.com/vb/ http://web.pdx.edu/~ruzickaa/meteorites/McSween/Fo-Qz.gif There is complete Mg-Fe solid solution between the pyroxenes, and as with most Mg-Fe solid solutions, the Mg-rich end members crystallize at higher temperatures than the Fe-rich end members. Inosilicate Minerals (clinopyroxenes) There are more options for ternary plots as there is more variability in cation composition Clinopyroxenes … and you are going to ♥ the phase diagram possibilities Inosilicate Minerals (clinopyroxene) Augite (Ca,Na)(Mg,Fe,Al)(Si,Al)2O6 Crystal: Monoclinic Pt. Group: 2/m Habit: columnar, massive, fibrous SG: 3.4; H: 5 to 6.5 L: vitreous; Str: green-grey Col: green-grey Clev: perfect [110], poor [010] Optics: Biaxial (+); bir = 0.0260 http://webmineral.com/data/Augite.shtml nα=1.68; nβ=1.684, nγ=1.706 Occurrence: basic igneous & metamorphic rocks From the Greek auge - "luster." Inosilicate Minerals (clinopyroxene) Augite (Ca,Na)(Mg,Fe,Al)(Si,Al)2O6 Crystal: Monoclinic Pt. Group: 2/m Habit: columnar, massive, fibrous SG: 3.4; H: 5 to 6.5 L: vitreous; Str: green-grey Col: green-grey Clev: perfect [110], poor [010] Optics: Biaxial (+); bir = 0.0260 http://www.mii.org/Minerals/photoaugite.html nα=1.68; nβ=1.684, nγ=1.706 Occurrence: basic igneous & metamorphic rocks From the Greek auge - "luster." Inosilicate Minerals (clinopyroxene) Spodumene [LiAlSi2O6] Crystal: Monoclinic Pt. Group: 2/m Habit: bladed SG: 3.15; H: 6.5-7 L: vitreous; Str: white Col: grey-white, yellow, pink Clev: [110] perfect; [100] good Optics: Biaxial (+); bir = 0.014-0.018 http://www.dkimages.com/discover/previews/867/70006667.JPG nα=1.648; nβ=1.655, nγ=1.662 From from the Greek, spodoumenos, "burnt to ash," Occurrence: Li-bearing pegmatites alluding to its color Inosilicate Minerals (clinopyroxene) Pigeonite 2+ [(Mg,Ca,Fe )Si2O6] Crystal: Monoclinic Pt. Group: 2/m Habit: prismatic SG: 3.38; H: 6 L: vitreous, dull; Str: white Col: green, brown Clev: [001], good http://webmineral.com/specimens/picshow.php?id=2262 Optics: Biaxial (+); bir=0.021-0.030 nα=1.683; nβ=1.684, nγ=1.704 Occurrence: shallow intermediate/ mafic intrusive igneous rocks Pigeonite http://www.tulane.edu/~sanelson/images/opx-cpxphasediag.gif Slow cooling allows pigeonite to convert to other orthopyroxenes Exsolution Inosilicate Minerals (clinopyroxene) Jadeite [NaAlSi2O6] Crystal: Monoclinic Pt. Group: 2/m Habit: columnar, fibrous SG: 3.3; H: 6.5 L: vitreous; Str: white Col: green, white, blue-grey, pale purple Clev: good [110] From Spanish, piedra de ijada, "stone of the Optics: Biaxial (+); bir = 0.006-0.021 side," because its supposed to cure kidney ailments if applied to the side of the body. nα=1.640; nβ=1.645, nγ=1.652 Occurrence: blueschist-type metamorphic rocks Inosilicate Minerals (clinopyroxene) Jade… Comes in 2 varieties 1) Jadeite (a pyroxene) 2) Nephrite jade or “actinolite”; (an amphibole) Inosilicate Minerals (pyroxenoids) Wollastonite [CaSiO3] Crystal: Triclinic Pt. Group: 1 Habit: massive, fibrous SG: 2.84; H: 5 L: silky; Str: white Col: white, yellow, grey, brown, red Clev: [100] perfect; [102] [001] good Optics: Biaxial (-); bir = 0.014-0.016 http://www.leescorp.com nα=1.615; nβ=1.627, nγ=1.629 Occurrence: metamorphosed limestone and dolostone Named after English mineralogist W. H. Wollaston (1766-1828). Inosilicate Minerals (pyroxenoids) Pectolite [NaCa2Si3O8(OH)] Crystal: Triclinic Pt. Group: 1 Habit: acicular, globular SG: 2.86; H: 5 L: silky; Str: white Col: white, grey, light green Clev: [001], [100] perfect Optics: Biaxial (+); bir = 0.032 http://csm.jmu.edu/minerals/minerals%5C+PectoliteVA.jpg nα=1.594; nβ=1.603, nγ=1.631 From the Greek pektos - "compacted" Occurrence: Secondary vug-filling mineral in basalt Inosilicate Minerals (pyroxenoids) Rhodonite 2+ [Mn(Fe ,Mg,Ca)SiO3] Crystal: Triclinic Pt. Group: 1 Habit: granular, tabular, massive SG: 3.6; H: 6 L: vitreous; Str: white Col: pink, rose red, yellow Clev: [110] perfect Optics: Biaxial (+); bir = 0.0130 http://www.webmineral.com/data/Rhodonite.shtml From the Greek rhodos - "rose colored." nα=1.711; nβ=1.714, nγ=1.724 Occurrence: Mn-bearing hydrothermal & metamorphic rocks Identifying Rock-forming Minerals What do? using your hand lens.... 1) distinguish how many different minerals you have in the rock 2) test the best representatives you can find • luster, cleavage, colour (easy) •hardness, streak (doable) •habit, specific gravity (unlikely) GY 302: Crystallography and Mineralogy Lecture 21: Silicates 4: Pyroxenes and Pyroxenoids Instructor: Dr. Doug Haywick [email protected] This is a free open access lecture, but not for commercial purposes. For personal use only. .