Lab 11 - Ca 2 Mg 5 Si 8 O 22 (OH) 2 Ca 2 Fe 5 Si 8 O 22...

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Lab 11 Optical properties of Pyroxenes and amphiboles 1- Determine the optical properties of the minerals listed below. Pull out the hand specimens of these samples and examine them simultaneously. Pyroxenes Enstatite Diopside Augite Jadeite (II-3) Omphacite (As-85) Amphiboles Tremolite Actinolite (93) Hornblende Glaucophane (As-85) Riebeckite Grunerite (100)
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Pyroxenes Orthopyroxenes Enstatite (+) Hypersthene Ferrosilite (-) Mg 2 Si 2 O 6 (Fe,Mg)Si 2 O 6 Fe 2 Si 2 O 6 Clinopyroxenes Pigeonite (+) (Fe,Mg,Ca)(Mg,Fe)Si 2 O 6 (32 – 44) Diopside (+) Hedenbergite (+) Ferrohedenbergite (-) CaMgSi 2 O 6 CaFeSi 2 O 6 (37 – 43°) (37 – 43°) Augite (+) Ca(Mg,Fe)(Al,Fe)(Al,Si) 2 O 6 (36 – 45°) Omphacite Aeg-augite (0 – 20°) (35 – 42°) Jadeite (+/-) Aegirine (Acmite) (+) NaAlSi 2 O 6 NaFeSi 2 O 6 (0 – 35°) (0 - 10°) Spodumene (+) LiAlSi 2 O 6 (22 – 26°)
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Amphiboles Orthoamphiboles Anthophyllite (-) Gedrite (+) Mg 7 Si 8 O 22 (OH) 2 Fe 7 Si 8 O 22 (OH) 2 Clinoamphiboles Cummingtonite (+) Grunerite (-) Mg 7 Si 8 O 22 (OH) 2 Fe 7 Si 8 O 22 (OH) 2 (20°) (10°) Tremolite (-) Actinolite Ferrotremolite (-)
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Unformatted text preview: Ca 2 Mg 5 Si 8 O 22 (OH) 2 Ca 2 Fe 5 Si 8 O 22 (OH) 2 (10 21) (10 21) Hornblende (-) (Na,K)Ca 2 (Mg,Fe,Al,Fe) 5 (Al,Si) 8 O 22 (OH) 2 (22 34) Glaucophane (-) Riebeckite (-) Na 2 Mg 3 Al 2 Si 8 O 22 (OH) 2 Na 2 Fe 3 Fe 2 Si 8 O 22 (OH) 2 (0 22) (0 21) Arfvedsonite (-) Na 3 Fe 4 AlSi 8 O 22 (OH) 2 (0 30) Differences between amphiboles and pyroxenes Pyroxenes Amphiboles Shape Short, stubby, prismatic, 8 sided in cross section Long, slender, prismatic, 6 sided in cross-section Cleavage 2 directional, 94 2 directional, 124 Color Weak color, weak pleochroism Strong colors, strong Pleochroism Relief High Moderate to high Birefringence Strong Moderate to strong Extinction straight or < 45 straight or < 25 Sign of elongation Lengthslow (usually) Lengthfast (usually) Optic sign usually negative usually positive...
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Lab 11 - Ca 2 Mg 5 Si 8 O 22 (OH) 2 Ca 2 Fe 5 Si 8 O 22...

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