Mike Horne FGS
Common minerals in thin section
Tutor - Mike Horne FGS
University of Hull
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Common minerals in thin section. |
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shape |
colour |
pleochroism |
Cleavage |
Relief |
Birefringence |
Twinning |
Extinction |
occurrence |
name |
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varies |
Clear |
None |
None |
Low |
Low 1st order |
None |
Sometimes strained |
Common |
quartz |
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Prismatic |
Clear |
none |
Good 2 @ 90 degs |
Low |
Low 1st order |
simple |
vary |
Igneous & Metam. |
orthoclase |
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multiple |
plagioclase |
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tartan |
microcline |
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Prismatic Or octagonal |
Pink, brown or green |
yes |
Good 2 @ 90 degs |
High |
1st - 2nd |
Sometimes |
45 degs |
Basic igneous,Metam. |
'Augite' |
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Prismatic |
Brown, green, yellow, bluish |
Some varieties |
Good 2 @ 124 degs |
High |
1st to mid-2nd |
Not common |
Up to 25 degs |
Acid/intermediate Ig., Metam. |
'Hornblende' |
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Platey |
Brown |
Strong |
V good |
Moderate |
High, masked |
Straight |
Ig. & Met. |
Biotite Mica |
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Platey |
Clear |
No |
V good |
Low - mod |
High 3rd |
Straight |
Granite,schists,mudrocks |
Muscovite Mica |
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Platey |
Green |
Strong |
Good |
Low |
Low, masked |
Straight |
Met., ironstones |
Chlorite |
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Prismatic |
Clear, yellow-brown |
Yes |
Poor, often cracked |
High or v high |
High 3rd |
Rare |
Straight |
Basic Ig. |
Olivine |
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Polygon, circle |
Clear, pale pink |
None |
None |
High |
None |
Not common |
N/A |
Metam. |
Garnet |
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Interlocking xtals |
Clear, yellow |
None |
Very good |
'twinkling' |
Very high |
Sometimes |
Marbles, limestone |
Calcite |
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copyright Mike Horne - October 2016
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