Oligoclase is a plagioclase feldspar, intermediate between albite and anorthite.
In thin section, plagioclase feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL). You can find the explanation on the plagioclase feldspar page.
Physical Properties |
|
| Chemical formula | (Na,Ca)(Si,Al)4O8 |
| Class | Tectosilicate 3D framework of linked tetrahedra |
| Crystal system | Triclinic |
| Habit | Prismatic Tabular Elongate Columnar Grainy Massive from minerals.net |
| Color | Colorless Brown Greenish Gray Yellowish |
| Hardness | 7 |
| Specific gravity | 2.65 |
| Cleavage | Perfect {001}, Good {010} |
| Fracture | Uneven |
| Luster | Vitreous |
| Transparency | Transparent to translucent |
| Streak | White |
Optical Properties |
|
| PPL | Colorless Non-pleochroic |
| XPL | 1st order gray |
| δ | 0.009 |
| after webmineral.com |
Oligoclase in Hand Sample
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Oligoclase in Thin Section
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