Anorthite identification and geology

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• Previous: Anhydrite — Anhydrous calcium sulfate that converts to gypsum when exposed to water. Common in evaporite sequences.
• Next: Antigorite — Platy serpentine mineral forming massive dense aggregates. Non-fibrous and generally considered safer to handle than chrysotile.
• Bytownite
• Labradorite
• Wollastonite

Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner

GeoMiner

Last updated

2026-03-30T14:36:45.035216+00:00

Review status

Published; not independently peer-reviewed

• IMA–CNMNC List of Mineral Names — International Mineralogical Association. Official mineral-name, nomenclature, and classification records.
• Mineral ID Key — Mineralogical Society of America. Physical-property identification methods, repeat-testing guidance, and limitations.

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Common questions

What is Anorthite?

Calcium end member of the plagioclase feldspar series. Relatively rare on Earth but abundant in lunar rocks.

How can you identify Anorthite?

Compare several properties rather than relying on colour alone. This entry records colour: White to gray; lustre: Vitreous; streak: White; Mohs hardness: 6-6.5; cleavage: Perfect in two directions; crystal system: Triclinic; transparency: Translucent to opaque. Confirm an important identification with additional field tests or qualified laboratory work.

How does Anorthite form?

Crystallizes from very calcium-rich magmas and in contact metamorphic zones around mafic intrusions.

Where is Anorthite commonly found?

Japan, Italy, India; found in volcanic rocks and contact metamorphic zones. Abundant on the Moon.

What is Anorthite commonly confused with?

Anorthite may be confused with Bytownite, Labradorite, Wollastonite. Compare multiple diagnostic properties because colour and surface appearance can overlap.