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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
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