Sanidine is an alkali feldspar intermediate in composition between albite and orthoclase.
In thin section, alkali feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL). You can find the explanation on the alkali feldspar page.
Physical Properties |
|
| Chemical formula | (K,Na)Si3O8 |
| Class | Tectosilicate 3D framework of linked tetrahedra |
| Crystal system | Monoclinic |
| Habit | Prismatic Tabular Elongate Often have square cross section |
| Color | White Variable |
| Hardness | 6 |
| Specific gravity | 2.56 |
| Cleavage | Perfect (001), good (010) |
| Luster | Vitreous |
| Transparency | Transparent to translucent |
| Streak | White |
Optical Properties |
|
| PPL | Colorless Low relief |
| XPL | 1st order gray |
| δ | 0.007 |
| Twinning | Carlsbad Manebach Baveno |
| after Perkins, 307 |
Sanidine in Hand Sample
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Sanidine in Thin Section
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