Lecture 20 (12/06/2006)Lecture 20 (12/06/2006)

Systematic Description of MineralsSystematic Description of Minerals

Part 4: Part 4: Silicates II: Cyclosilicates, Silicates II: Cyclosilicates,

Inosilicates, Phyllosilicates and Inosilicates, Phyllosilicates and TectosilicatesTectosilicates

Silicate Mineral ClassificationSilicate Mineral Classification(based on arrangement of SiO(based on arrangement of SiO44 tetrahedra) tetrahedra)

Cyclosilicates (Ring)Cyclosilicates (Ring) x(SiOx(SiO33) Unit Composition ) Unit Composition Hexagonal and Orthorhombic (pseudohexagonal) Hexagonal and Orthorhombic (pseudohexagonal)

symmetries most commonsymmetries most common Forms silicate minerals with: Forms silicate minerals with:

Moderate density(2.6-3.2) and hardness (7-8)Moderate density(2.6-3.2) and hardness (7-8)Prismatic habitsPrismatic habitsPoor cleavagePoor cleavage

BerylBeryl

Common CyclosilicatesCommon Cyclosilicates

BerylBeryl BeBe33AlAl22(Si(Si66OO1818))Common accessory mineral in granite pegmatiteCommon accessory mineral in granite pegmatite

Gem varieties – Aquamarine, Emerald, Rose Beryl, Gem varieties – Aquamarine, Emerald, Rose Beryl, Golden BerylGolden Beryl

CordieriteCordierite (Mg,Fe)(Mg,Fe)22AlAl44SiSi55OO1818··nnH20H20

Common mineral in contact metamorphosed Common mineral in contact metamorphosed argillaceous rocksargillaceous rocks

Resembles quartz in appearance and hardness (7-7.5)Resembles quartz in appearance and hardness (7-7.5)

TourmalineTourmaline (Na,Ca)(Na,Ca)(Li,Mg,Al)(Li,Mg,Al)33(Al,Fe,Mn)(Al,Fe,Mn)66(BO(BO33))33 (Si(Si66OO1818))(OH)(OH)44

Common accessory mineral in granite pegmatiteCommon accessory mineral in granite pegmatite

Characteristic striated prisms with trigonal outlineCharacteristic striated prisms with trigonal outlinewatermelonwatermelontourmalinetourmaline

Inosilicates (Chain)Inosilicates (Chain) x(SiOx(SiO33) Unit Composition ) Unit Composition Single and double silicon tetrahedra chainsSingle and double silicon tetrahedra chains Typically monoclinic and orthorhombic symmetryTypically monoclinic and orthorhombic symmetry Single chains (Pyroxenes) develop ~90° cleavageSingle chains (Pyroxenes) develop ~90° cleavage Double chains (Amphiboles) develop 120 ° cleavageDouble chains (Amphiboles) develop 120 ° cleavage

Amphibole Amphibole StructureStructure

Pyroxene Pyroxene StructureStructure

Pyroxenes (XYZPyroxenes (XYZ22OO6 6 ))X (MX (M22) – Na, Ca, Mn, Fe) – Na, Ca, Mn, Fe+2+2, Mg, Li , Mg, Li

Y (M Y (M11) – Mn, Fe) – Mn, Fe+2+2, Mg, Fe, Mg, Fe+3+3, Cr, Cr+3 +3 , Ti, Ti+4+4

Z (Tetrahedral site) - AlZ (Tetrahedral site) - Al+3+3, , SiSi+4+4

ClinopyroxenesClinopyroxenes

OrthopyroxenesOrthopyroxenes

Exsolution in PyroxeneExsolution in Pyroxene

Exsolved compExsolved comp

Original compOriginal comp

Amphiboles (AAmphiboles (A0-10-1XX22YY55ZZ88OO22 22 (OH,F))(OH,F))A – Na, KA – Na, K

X (MX (M44) – Na, Ca, Mn, Fe) – Na, Ca, Mn, Fe+2+2, Mg, Li , Mg, Li

Y (M Y (M1-31-3) – Mn, Fe) – Mn, Fe+2+2, Mg, Fe, Mg, Fe+3+3, Cr, Cr+3 +3 , Ti, Ti+4+4

Z (Tetrahedral site) - AlZ (Tetrahedral site) - Al+3+3, , SiSi+4+4

Common Types of AmphibolesCommon Types of Amphiboles

Phyllosilicates (Sheet)Phyllosilicates (Sheet) x(Six(Si22OO55) Unit Composition ) Unit Composition Infinite sheets of silicon tetrahedraInfinite sheets of silicon tetrahedra Strong single cleavage parallel to silicon Strong single cleavage parallel to silicon

sheetssheets

PyrophyllitePyrophyllite MuscoviteMuscovite

Phyllosilicate Phyllosilicate StructuresStructures

Alternating Si Alternating Si Tetrahedral and Tetrahedral and

Octahedral layers Octahedral layers bound by large cations bound by large cations or weak electrostatic or weak electrostatic

bondsbonds

Common PhyllosilicatesCommon Phyllosilicates

AntigoriteAntigorite

ChrysotileChrysotileKaoliniteKaolinite

TalcTalc

PyrophyllitePyrophyllite

MuscoviteMuscovite

LepidoliteLepidolite

BiotiteBiotiteChloriteChlorite

Tectosilicates (Framework)Tectosilicates (Framework)

x(SiOx(SiO22) Unit Composition ) Unit Composition 3-D framework of linked 3-D framework of linked

silicon tetrahedrasilicon tetrahedra Variable physical Variable physical

properties and properties and symmetries depending symmetries depending on linkage of framework on linkage of framework groupingsgroupings

SiOSiO22 Group Group

Opal SiOOpal SiO22·nH·nH22OO

Quartz SiOQuartz SiO22

Feldspar GroupFeldspar Group

Alkali FeldsparsAlkali Feldspars

Perthite (albite exsolution in microcline)Perthite (albite exsolution in microcline)

Plagioclase FeldsparsPlagioclase Feldspars

Albite TwinningAlbite Twinning

Compositional Compositional ZoningZoning(Oscillatory)(Oscillatory)

Feldspathoids (Si-poor feldspars)Feldspathoids (Si-poor feldspars)Common in alkaline (Si-undersaturated) igneous rocksCommon in alkaline (Si-undersaturated) igneous rocks

Leucite – KAlSiOLeucite – KAlSiO44

Nepheline – (Na,K)AlSiONepheline – (Na,K)AlSiO44

Sodalite – NaSodalite – Na88(AlSiO(AlSiO44))66ClCl22

Hydrous TectosilicatesHydrous Tectosilicates

Analcime (Scapolite Gp) Analcime (Scapolite Gp) NaAlSiNaAlSi22OO66·H·H22OO

Natrolite (Zeolite Gp) Natrolite (Zeolite Gp) NaNa22AlAl22SiSi33OO1010·2H·2H22OO

Heulandite (Zeolite Gp) Heulandite (Zeolite Gp) CaAlCaAl22SiSi77OO1818·6H·6H22OO

Stilbite (Zeolite Gp) Stilbite (Zeolite Gp) NaCaNaCa22AlAl55SiSi1313OO3636·14H·14H22OO

Next Lecture 12/11/06Next Lecture 12/11/06

Introduction to X-ray DiffractometryIntroduction to X-ray Diffractometry

Read: Klein p. 309-321Read: Klein p. 309-321

12/13 – Final Review: Mineralogy Trivia12/13 – Final Review: Mineralogy Trivia