Moonstone

Orthoclase · KAlSi₃O₈. Colors: colorless to white, gray, green, peach, brown; blue sheen.

By Maxime PerriardLast reviewed September 2026

Browse the market In the encyclopedia

Mohs: 6–6.5
RI: 1.518–1.526
SG: 2.58
Crystal system: monoclinic

(Fig. 01)Stone record

Moonstone at a glance.

Moonstone specimen — Photo: Smithsonian NMNH · CC0

Species: Orthoclase
Formula: KAlSi₃O₈
Crystal system: monoclinic
Mohs: 6–6.5
RI: 1.518–1.526
SG: 2.58
Colors: colorless to white, gray, green, peach, brown; blue sheen

(Fig. 02)In the encyclopedia4

What the encyclopedia says.

4 passages, quoted as published. Each links to the full entry and the sources of its chapter.

02.13 · Stones
Turquoise, lapis lazuli, malachite and feldspars
Feldspars supply three phenomenal gems. Moonstone is orthoclase intergrown with albite in stacked alternating layers; light scattered between them produces adularescence. Labradorite and sanidine can show it too, and Madagascar labradorite is sold as rainbow moonstone. Labradorite is named for Labrador in Canada, and sunstone glitters from tiny platelets, or from copper in Oregon material.
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03.07 · Science
Stars, cat’s-eyes, play-of-color and adularescence
Play-of-color in precious opal is diffraction. Silica spheres of uniform size, stacked in orderly arrays that behave as three-dimensional photonic crystals, split white light into patches of pure spectral color that change with viewing angle. Smaller spheres give blue and violet; larger ones give red, orange and green. Adularescence is the soft, floating bluish-white sheen of moonstone, which is built from alternating layers of orthoclase and albite feldspar. Light scatters between these microscopic layers and interferes, and the thinner and more uniform the layers, the stronger the effect.
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20.08 · History
Literature and film
Fiction often treats a gem as the object everyone wants, which lets a story pass it from hand to hand. Wilkie Collins's The Moonstone (1868), serialized in Charles Dickens's magazine All the Year Round, concerns a sacred Indian diamond seized during the 1799 siege of Seringapatam. Left to a young Englishwoman, Rachel Verinder, it vanishes on the night of her eighteenth birthday, and several narrators, along with Sergeant Cuff of Scotland Yard, try to explain the theft. T. S. Eliot later ranked it as the first and best of modern English detective novels.
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22.02 · Ownership
Cleaning, storage and wearability
Ultrasonic cleaners loosen dirt with high-frequency vibration, and steam cleaners blast it away with hot pressurized steam. Both can widen fractures, split stones along cleavage, drive out the oils or resins used as fillers and shock heat-sensitive gems. GIA's gem-by-gem guidance, summarized in the table, treats warm soapy water and a soft brush as the safe method for nearly all gems. It calls both machines safe for untreated or heat-treated ruby and sapphire and advises against them for emerald, opal, pearl, tanzanite, turquoise and moonstone. The safe, caution and avoid ratings in that table are this encyclopedia's own three-way scheme, mapped from GIA's wording rather than published by GIA. For diamonds, GIA advises against both at home because vibration can loosen stones in their settings.
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