gemstone
Moonstone Cabochon
Orthoclase Feldspar ((K,Na)AlSi3O8) with Albite lamellae
Hardness: 6.0-6.5 Mohs; Color: White to semi-transparent with blue or white adularescence (sheen); Luster: Vitreous to Pearly; Crystal Structure: Monoclinic; Specific Gravity: 2.56-2.59
- Hardness
- 6
- Luster
- Vitreous to Pearly
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Physical properties
Hardness: 6.0-6.5 Mohs; Color: White to semi-transparent with blue or white adularescence (sheen); Luster: Vitreous to Pearly; Crystal Structure: Monoclinic; Specific Gravity: 2.56-2.59
Formation & geological history
Formed in plutonic igneous rocks (pegmatites) where cooling occurs slowly, allowing intergrowths of orthoclase and albite. This microscopic layered structure causes the scattering of light (adularescence).
Uses & applications
Primarily used in jewelry as cabochons, beads, or carvings. Highly valued in spiritual and decorative gem collections.
Geological facts
The unique play of light, called adularescence, is caused by light reflecting from internal layers of different feldspar minerals. In ancient Rome, it was believed moonstones were formed from frozen moonlight.
Field identification & locations
Identify by its characteristic billowy light effect (adularescence) that moves as the stone is rotated. Distinct from opal or glass by its hardness and internal cleavage planes. Common sources include Sri Lanka, India, and Madagascar.
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