Moonstone (Feldspar)
Moonstone is a member of the Feldspar Group of minerals that also includes Albite, Amazonite, Andesine, Anorthite, Bytownite, Hyalophane, Labradorite, Moonstone, Oligoclase, Orthoclase, Sanidine, and Sunstone. Moonstone is a popular name for Orthoclase and/or Plagioclase Feldspar showing a blue sheen. The blue sheen is produced by the presence of very finely dispersed Albite crystals or plates within a body of Orthoclase or Labradorite. This blue sheen is referred to as adularescence. Blue sheen Moonstone with a colorless and transparent body free of inclusions makes for a rare and beautiful gem. Common Moonstone is usually translucent to opaque or heavily included.
Moonstone gets its name from its blueish glow due to adularescence. The name Orthoclase is from the Greek words orthos meaning right and kalo meaning I cleave because its cleavages are at right angles. Feldspar is from the Swedish Feldt + spat meaning that it was found in fields overlying granite.
| Category: | Feldspar variety |
| Formula: | (Na,K)AlSi3O8 |
| sodium potassium aluminium silicate | |
| Crystallography: | Monoclinic – Prismatic |
| Cleavage: | Perfect |
| Fracture: | uneven to conchoidal |
| Hardness (Mohs): | 6.0 |
| Density: | 2.56 to 2.61 |
| Color: | Can be numerous colors, including blue, grey, white, pink, peach, green and brown, as well as colorless |
| Transparency: | Transparent,Translucent |
| Luster: | Opalescent |
| Refractive Index: | 1.518 to 1.527 (Biaxial / – ) |
| Birefringence: | 0.006 to 0.007 |
| Dispersion: | None |
| Pleochroism: | Absent |
