Black Moonstone Identification Guide
Identify black moonstone, a dark feldspar showing adularescence and sometimes flash, using its sheen, cleavage, hardness, and contrast with labradorite and obsidian.
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What Black Moonstone Looks Like
Black moonstone is a dark-bodied feldspar (typically a plagioclase, often from the labradorite-andesine range, sometimes orthoclase-bearing) that displays a soft floating sheen called adularescence. Bodies range from smoky gray to charcoal and near-black, frequently mottled with cream, peach, or silvery flecks.
- Color: gray-black to deep charcoal, often with lighter speckling
- Optical effect: silvery-blue to white adularescence (a billowy glow) that shifts as you tilt it; some show colored flash
- Luster: vitreous to slightly pearly
- Transparency: translucent to nearly opaque
- Habit: massive or as cleavable blocky pieces
Step-by-Step Field-ID Checklist
- Rock it under light. Look for a glow or sheen that floats across the surface and moves with the stone — that adularescence/schiller is the key feldspar clue.
- Find cleavage. Look for two flat cleavage directions meeting near 90° and a stepped, blocky break.
- Hardness test. Feldspar is Mohs 6–6.5; it scratches glass but a quartz point will scratch it.
- Check streak. White streak.
- Inspect for speckles. Peachy/cream mottling is common in black moonstone.
Key Diagnostic Tests
- Mohs hardness: 6–6.5 (softer than quartz).
- Streak: white.
- Cleavage: two good cleavages intersecting at ~90° — diagnostic of feldspar and a key separator from quartz and glass.
- Specific gravity: ~2.55–2.70.
- No acid reaction; not magnetic.
- Sheen vs surface: adularescence appears to come from beneath the surface, unlike a simple polish shine.
Common Look-Alikes and How to Tell Them Apart
- Labradorite: closely related feldspar but shows broad, vivid spectral color flashes (labradorescence) rather than a soft blue-white billow; the two grade into each other and 'black moonstone' often is plagioclase near labradorite.
- Obsidian (incl. sheen/rainbow obsidian): volcanic glass with no cleavage and a conchoidal fracture; any sheen sits flat in one direction, and obsidian shows no stepped cleavage.
- Black onyx/chalcedony: harder (7), no adularescence, no cleavage, conchoidal fracture.
- Smoky quartz: harder (7), no cleavage, transparent-to-smoky with no floating sheen.
- Hematite/dyed stones: opaque, no internal glow; hematite gives a red streak.
The decisive combination is adularescent sheen + two cleavages near 90° + hardness ~6: only feldspar fits all three. Glass and quartz lack the cleavage; quartz is also harder.
Where Black Moonstone Is Found
Much black moonstone on the market comes from India and Madagascar, with feldspar sources also in Sri Lanka, Tanzania, and the USA. It forms in igneous rocks (especially intermediate plutonic rocks and pegmatites) and is recovered from weathered deposits and gravels.
Quick Confirmation
A dark gray-to-black stone with a soft floating blue-white sheen, two cleavage planes near 90°, hardness ~6, and a white streak is black moonstone (a dark feldspar) rather than obsidian or chalcedony.
Frequently asked questions
How can you tell if black moonstone is real?
Genuine black moonstone is feldspar: it shows a floating blue-white adularescent sheen, has two cleavage directions meeting near 90°, a hardness of 6–6.5 (a quartz point will scratch it), and a white streak. No cleavage and a conchoidal fracture point to glass or chalcedony instead.
What does black moonstone look like?
It is a dark gray to charcoal or near-black feldspar, often mottled with cream or peach speckles, that displays a soft silvery-blue glow which floats across the surface as you tilt it. Some pieces also flash color.
Black moonstone vs labradorite — what is the difference?
They are closely related plagioclase feldspars and grade into one another. Labradorite shows broad, vivid spectral color flashes (labradorescence), while black moonstone shows a softer blue-white billowing sheen (adularescence). Much 'black moonstone' is plagioclase near the labradorite range.
Is black moonstone the same as black obsidian?
No. Black moonstone is crystalline feldspar with cleavage and adularescence. Obsidian is amorphous volcanic glass with no cleavage and a conchoidal fracture. Look for cleavage planes and a floating internal glow to confirm moonstone.