Yellow-green Sanidine crystal from the small finds at Itrongay, Madagascar. Weighs 20 grams or 100 carats. By Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC-BY-SA-3.0], via Wikimedia Commons
Sanidine Information
| Data | Value |
|---|---|
| Name | Sanidine |
| Is a Variety of | Orthoclase |
| Colors | Colorless, sometimes brown or yellow. |
| Crystallography | Monoclinic. |
| Refractive Index | 1.516-1.526 |
| Luster | Vitreous. |
| Hardness | 6-6.5 |
| Wearability | Poor |
| Fracture | Uneven to splintery, Parting common |
| Specific Gravity | 2.57-2.58 |
| Birefringence | 0.003-0 .007 |
| Cleavage | Perfect and easy in two directions |
| Dispersion | None. |
| Luminescence | None. |
| Luminescence Present | No |
| Transparency | Transparent to translucent. |
| Absorption Spectrum | Not diagnostic. |
| Pleochroism |
None. |
| Optics |
Biaxial (-). 2V = 18-54º. |
| Optic Sign | Biaxial - |
Comments
Sanidine is a mineral of volcanic rocks, with little gem significance. It is uncommon and rarely seen as a gem. While occasionally brown or yellow, most examples are colorless. While the properties are closer to microcline, it is usually classed as a plagioclase.
Name
Sanidine is also from the Greek, sanis, meaning board, in reference to the tabular crystals. Anorthoclase is from Greek words for not upright because the cleavage is not 90°.
Occurrence
- A component of acid igneous rocks. Oregon; California.
- Near Koblenz, Germany: brown transparent gems; S.G. 2.57-2.58; birefringence 0.007; indices: 1.516-1.520/ 1.520-1.525/1.522-1.526.
- Ashton, Idaho: sanidine crystals in volcanic luff, up to 1 cm, colorless, well formed. Indices: 1.516-1.519/ 1.520-1.522/1.521-1.523; 2V=8-19°; birefringence 0.003-0.005.
Stone Sizes
Sanidine is not a common mineral and is hardly ever seen as a gemstone. Crystals tend to be colorless and nondescript and are rare in cuttable sizes.
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