Grey Moonstone Identification Guide

What Grey Moonstone Looks Like

Grey moonstone is a feldspar (typically orthoclase intergrown with albite, or a plagioclase) prized for adularescence — a soft, floating blue-to-white sheen that seems to glow from beneath the surface. The body color is a smoky, semi-transparent to translucent grey, sometimes nearly steel or champagne. Luster is vitreous to slightly pearly, and the sheen moves as you tilt the stone, a hallmark called schiller.

• Color: grey, smoke, silvery, occasionally with a faint bluish or peachy cast
• Transparency: translucent to semi-transparent
• Luster: vitreous, pearly on cleavage surfaces
• Habit: blocky cleavage fragments; cut as cabochons to focus the sheen

Step-by-Step Field-ID Checklist

1. Tilt for adularescence. Rock the stone under a single light source. Real moonstone shows a mobile blue or white billow that glides across the dome — not a fixed surface glitter.
2. Check the body tone. A genuinely grey (not white) translucent feldspar with internal glow points to grey moonstone.
3. Look for cleavage. Two cleavage directions meeting near 90° are diagnostic of feldspar.
4. Test hardness. It should scratch glass but be scratched by quartz.
5. Inspect for centipede inclusions. Tiny stress cracks ("centipedes") are common and confirm natural feldspar.

Key Diagnostic Tests

• Mohs hardness: 6–6.5. Scratches glass; quartz (7) scratches it.
• Streak: white.
• Cleavage: perfect in two directions at roughly 90° — the strongest feldspar clue.
• Fracture: uneven to conchoidal between cleavages.
• Specific gravity: ~2.55–2.6 — light in the hand.
• Optical effect: adularescence (sheen from lamellar intergrowth), distinct from the spectral flashes of labradorescence.

Common Look-Alikes and How to Tell Them Apart

• Rainbow moonstone (labradorite): shows multicolored flashes (blue, green, gold) rather than a single soft blue billow; it is technically labradorite, with a more vivid, directional flash.
• Grey chalcedony / agate: lacks adularescence and cleavage, is harder (7), and has conchoidal fracture only.
• Opalite (man-made glass): shows blue glow over a milky body but has no cleavage, contains gas bubbles, and gives a warm orange glow in transmitted light.
• Grey labradorite: broader metallic schiller and visible twinning striations; heavier feel.
• Smoky quartz: transparent, hexagonal, hardness 7, and never shows adularescence.

The single most reliable separator is combining the soft mobile sheen with two-direction cleavage at ~90° and a hardness below quartz.

Where Grey Moonstone Is Found

Gem-quality grey moonstone comes chiefly from Sri Lanka and India, with additional material from Madagascar, Myanmar, and Tanzania. It forms in pegmatites and feldspar-rich igneous and metamorphic rocks, often recovered as waterworn pebbles in placer gravels where the durable feldspar survives weathering.

Quick Field Summary

If a smoky-grey translucent stone glows with a floating blue sheen, breaks along two near-right-angle cleavages, scratches glass but not quartz, and feels light, you are almost certainly holding grey moonstone rather than chalcedony or imitation glass.