Moonstone (gemstone)
| Moonstone | |
|---|---|
| General | |
| Category | Tectosilicate minerals |
| Group | Feldspar group |
| Series | Alkali feldspar series |
| Formula | (Na,K)AlSi3O8 |
| IMA status | Variety of orthoclase |
| Crystal system | Monoclinic |
| Identification | |
| Color | Various, including blue, gray, white, pink, peach, green, and brown, as well as colorless |
| Cleavage | Perfect |
| Fracture | Uneven to conchoidal |
| Mohs scale hardness | 6.0–6.5 |
| Luster | Vitreous, opalescent |
| Streak | White |
| Specific gravity | 2.54–2.66 |
| Optical properties | For orthoclase and sanidine, biaxial (–); for oligoclase, biaxial +/– |
| Refractive index | 1.518–1.547 |
| Birefringence | 0.005–0.01 |
| Dispersion | 0.012 |
Moonstone is a sodium potassium aluminium silicate ((Na,K)AlSi3O8) of the feldspar group that displays a pearly and opalescent schiller. An alternative name for moonstone is hecatolite (from goddess Hecate).