Moonstone
Moonstone is a silicate mineral prized by collectors for its exceptional color range.
About Moonstoneextended article
Moonstone is the gem variety of feldspar celebrated for adularescence — a soft, billowy sheen of light that seems to float beneath the surface and move as the stone is turned. The effect arises from light scattering off microscopic alternating layers of two feldspars (typically orthoclase and albite) that unmixed as the crystal cooled.
Properties
Moonstone is most often a potassium feldspar close to orthoclase; it is monoclinic, moderately hard (6–6.5) and has two good cleavages. The most prized stones are near-colourless and transparent with a vivid blue sheen, though 'rainbow moonstone' (a labradorite) shows multicoloured flashes.
Occurrence
Sri Lanka and India are the historic sources of fine blue-sheen moonstone; Myanmar, Madagascar and Tanzania also produce gem material.
About Moonstone
Moonstone is a silicate mineral in the alkali feldspar group (orthoclase or adularia variety with adularescence) and has the chemical formula K(AlSi3O8) [orthoclase/adularia with albite lamellae]. It crystallizes in the monoclinic system and is one of the most visually varied minerals in the collector market. Its combination of structural character and global distribution make it a recognized species in both systematic and aesthetic collections.
Identification & care
Specimens usually show massive/alluvial; tabular crystals rare; polished cabochons are the primary form for collectors. Its color range is broad, including colorless, white, cream, grey, orange, brown, green, with blue, white, and or silver adularescence (sheen). The luster is vitreous, sub-vitreous, pearly, the streak is white, and specimens range from transparent to translucent. The cleavage is perfect on {001}, good on {010} — feldspar cleavage. The fracture is conchoidal, uneven, which aids identification.
Collector context
How it forms
The geological setting for Moonstone is typically granitic pegmatites and aplites; also in low-temperature hydrothermal deposits; concentrated in alluvial gem gravels through weathering. It is commonly found in association with albite, orthoclase, quartz, corundum (ruby/sapphire), spinel, tourmaline.
Why collectors care
Collectors pursue Moonstone for the clarity of its crystal form and, in good material, saturated color that reads instantly across a display case. A well-terminated moonstone on clean matrix photographs well, identifies quickly, and anchors a cabinet piece. Top Chinese specimens over the last two decades have reset the bar for what moonstone looks like at collector grade.
What affects value
Value in Moonstone is assessed, in typical order of weight, against: (1) locality provenance; (2) size relative to the species norm; (3) crystal form and termination sharpness; (4) color saturation and zoning; (5) transparency and internal clarity; (6) matrix quality and aesthetic balance; (7) condition (absence of damage, chips, or repair). Cleaning quality and verified locality documentation act as multipliers across the above.
Naming history
The name Moonstone has a specific etymological and historical context — see Mindat's reference entry for provenance details. We have retained naming data at the record level; published prose is paraphrased from factual fields rather than copied from source.
Frequently asked questions
What is Moonstone?
Moonstone is a silicate mineral prized by collectors for its exceptional color range.
What is the chemical formula of Moonstone?
The chemical formula of Moonstone is (K,Na)AlSi3O8.
References & databases
Mindat.org is the world’s largest open mineralogy database. Our descriptions are written independently and fact-checked.