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Anorthite
Anorthite is tectosilicate (plagioclase feldspar), CaAl₂Si₂O₈. In the hand, it rates 6 to 6.5 on the Mohs scale, and it runs colorless and white. The calcium-rich end of the plagioclase family, blocky pale crystals with feldspar's right-angle cleavage flash, rarer in collections than its siblings.
The geology.
Anorthite carries the formula CaAl₂Si₂O₈. It belongs to the triclinic system. Catalogues list it as tectosilicate (plagioclase feldspar).
It sits at 6 to 6.5 on the Mohs scale. The surface reads vitreous. Light behaviour is transparent to translucent. Specific gravity runs 2.72 to 2.76. The streak is white. It breaks with two cleavages near 90°.
The calcium-rich end of the plagioclase family, blocky pale crystals with feldspar's right-angle cleavage flash, rarer in collections than its siblings.
It reaches buyers as blocky crystals in volcanic ejecta, granular masses or rock-forming grains.
The origins.
Calcium-rich volcanic rocks; classic crystals from Miyakejima (Japan), Vesuvius (Italy); the dominant mineral of lunar highlands.
On value, the database notes: inexpensive grains; sharp Japanese crystals are collector items.
Traditional associations.
In energy work traditions, anorthite has little established lore; collectors prize it as the Moon-crust feldspar.
We keep this section because people ask. It sits below the geology on purpose, and none of it describes something the stone does.
Spotting the real thing.
The calcium-rich end of the plagioclase family, blocky pale crystals with feldspar's right-angle cleavage flash, rarer in collections than its siblings.
| Looks like | How to tell them apart |
|---|---|
| Albite | The sodium end-member, indistinguishable by eye; density and lab tests separate them |
| Quartz | No cleavage flash, slightly harder |
| Calcite | Fizzes and far softer |
At-home tests.
Before anyone talks you into a lab report, these are the checks worth doing yourself on anorthite.
| Test | What you should see |
|---|---|
| By eye | Right-angle cleavage flashes |
| Scratch check | Scratches glass with effort |
| By weight | Slightly denser than other feldspars (SG ~2.75) |
Stop short of anything that leaves a mark. A gemologist can answer the rest without damaging the stone.
Care & handling.
At 6 to 6.5 on the Mohs scale it handles careful wear but scratches against quartz and dust. Store it separately and take rings off before rough work.
It breaks with two cleavages near 90°, which is worth knowing before you set it or drop it.
Skip the ultrasonic. Lukewarm water, mild soap and a soft cloth handle routine cleaning without risk.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is CaAl₂Si₂O₈. Crystal system: Triclinic. Specific gravity: 2.72 to 2.76. Streak: White. Cleavage and fracture: Two cleavages near 90°.
How it reaches the market
Calcium-rich volcanic rocks; classic crystals from Miyakejima (Japan), Vesuvius (Italy); the dominant mineral of lunar highlands.
What it gets confused with
Albite: The sodium end-member, indistinguishable by eye; density and lab tests separate them. Quartz: No cleavage flash, slightly harder. Calcite: Fizzes and far softer.
What it is worth
Inexpensive grains; sharp Japanese crystals are collector items.
One more thing
The Moon's bright highlands are essentially anorthite, floated crystal scum from a global magma ocean 4.4 billion years ago.
An education-first guide.
We do not carry anorthite. This page exists because the question comes up and the honest answer is worth writing down, whether or not there is anything here to sell you.
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