RocksdayAnorthite vs Labradorite
To tell Anorthite from Labradorite: Labradorite is a mid-series plagioclase and often flashes blue.
The calcium end of the plagioclase feldspars. Albite is the sodium end; labradorite sits in between.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
A gray plagioclase feldspar that flashes electric blue, green and gold when light hits it at the right angle.
Photo: Parent Géry, Public domain
Key differences
- Labradorite is a mid-series plagioclase and often flashes blue.
Side by side
| Property | Anorthite | Labradorite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 6–6.5 | 6–6.5 |
| Luster | Vitreous | Vitreous |
| Streak | White | White |
| Colors | White, Gray | Gray, Black, Blue |
| Crystal system | Triclinic | Triclinic |
| Specific gravity | 2.74–2.76 | 2.68–2.72 |
| Formula | CaAl₂Si₂O₈ | (Ca,Na)(Al,Si)₄O₈ |
| Found in | Miyake-jima, Japan; Mount Vesuvius, Italy | Labrador, Canada; Finland |
Properties that are the same for both are grayed out.
How to identify anorthite
- White to gray blocky crystals with feldspar cleavage.
- Hardness about 6.
- Heavier than albite. Often in calcium-rich volcanic rocks or anorthosite.
Crystal system: Triclinic
Full Anorthite guide →How to identify labradorite
- Dull gray until tilted — then a vivid blue/green flash.
- Fine parallel lines on cleavage faces.
- Hardness about 6.
- Flash only appears from one direction.
Crystal system: Triclinic
Full Labradorite guide →More comparisons
Frequently asked questions
What is the difference between anorthite and labradorite?
Anorthite is a mineral (CaAl₂Si₂O₈) with a Mohs hardness of 6–6.5 and a vitreous luster, usually white or gray. Labradorite is a mineral with a Mohs hardness of 6–6.5 and a vitreous luster, usually gray, black or blue.
How can you tell anorthite from labradorite?
Labradorite is a mid-series plagioclase and often flashes blue.
Could you tell them apart from a blurry close-up?
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