MOST IMPORTANT MINERAL SUITE the silicate minerals

Inosilicates - Chains Single Chains Pyroxenes SiO3 or Si2O6 in Formula... Pyroxenes and Cations... Silica Chains and Octahedra... Two Sites in Pyroxenes... • Rhodonite and Pyroxmangite M

MOST IMPORTANT MINERAL

Nesosilicates - Isolated Tetrahedra

Sorosilicates - Paired Tetrahedra

•Epidote is the most common example

•Lawsonite

•Vesuvianite

Si2O7 in Formula

Inosilicates - Chains

Single Chains (Pyroxenes) SiO3 or Si2O6 in Formula

More Realistic Picture

Other Pyroxenes

• Sodic

– Jadeite: NaAlSi2O6

• Breakdown of Na-Feldspar

• High Pressure Metamorphism

– Aegerine (Acmite) NaFe3Si2O6

• Spodumene: LiAlSi2O6

– Pegmatite Mineral

Pyroxenes and Cations

Silica Chains and Octahedra

Two Sites in Pyroxenes

• Rhodonite and Pyroxmangite (MnSiO3)

– Mn is a good match in size and charge for Fe and Mg

– Pure Mn true pyroxenes exist

– These have complex chains because of variable compositions

Wollastonite CaSiO3

Wollastonite End-On

Rhodonite

Pyroxmangite

Inosilicates - Chains

Double Chains (Amphiboles Si4O11 in Formula)

Major Amphiboles

• Anthophyllite (Mg,Fe)7Si8O22(OH)2)

• Cummingtonite (Fe2Mg5Si8O22(OH)2) -Grunerite (Fe7Si8O22(OH)2)

• Tremolite (Ca2Mg5Si8O22(OH)2) – Actinolite

(Ca2(Mg,Fe)5Si8O22(OH)2)

• Hornblende (X2-3Y5Z8O22(OH)2)

• Glaucophane (Na2Mg3Al2Si8O22(OH)2) and

Riebeckite (Na2Fe++3,Fe+++2Si8O22(OH)2)

Beyond Amphiboles

• There are a few 3-chain and mixed chain silicates

• Discovered only in 1970’s

• Occur in asbestos

Phyllosilicates – Sheets (Si2O5 in Formula)

Tectosilicates - Dimensional Networks

Three-• Quartz Feldspars

K-Feldspars and Mixtures

• K-Feldspars (KAlSi3O8)

– Microcline (Slow cooling)

– Orthoclase (Faster cooling)

– Sanidine (Fastest cooling, High T)

• Anorthoclase: Solid solution of K-Feldspar and

Albite (NaAlSi3O8)

• Perthite: K-Feldspar with exsolved plagioclase

• Antiperthite: Plagioclase with exsolved K-Feldspar

• 30-50% An = Andesine: Andesites and Diorite

• 50-70% An = Labradorite: Basalt and Gabbro

• 70-90% An = Bytownite: Rarest

• 90-100% An = Anorthite: Metamorphic

Feldspathoids (Foids)

• Fill “ecological niche” of feldspars in Si-poor rocks

• Never occur with quartz

• Leucite (KAlSi2O6)

• Nepheline ((Na,K)AlSiO4)

Scapolites and Relatives

• Sodalite (Na8(AlSiO4)6Cl2)

• Lazurite (Na,Ca)8(AlSiO4)6(SO4,S,Cl)2)

• Scapolite

– Marialite = Albite + NaCl

– Meionite = Anorthite + CaSO4 or CaCO3