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Biotite
Biotite is phyllosilicate (mica), K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂. In the hand, it rates 2.5 to 3 on the Mohs scale, and it runs black and dark brown. Dark mica that peels into thin flexible glittery sheets with a fingernail. Granites, schists, and gneisses worldwide, one of the most common dark minerals.
The geology.
Biotite carries the formula K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂. It belongs to the monoclinic system. Its listing category is phyllosilicate (mica).
It sits at 2.5 to 3 on the Mohs scale. The surface reads vitreous to pearly. Light behaviour is translucent in thin sheets. Specific gravity runs 2.8 to 3.4. The streak is white to gray. It breaks with perfect basal cleavage, peels into flexible sheets.
Dark mica that peels into thin flexible glittery sheets with a fingernail.
It turns up mostly as mica 'books', flakes in granite and schist or sheet specimens.
The origins.
Granites, schists, and gneisses worldwide, one of the most common dark minerals.
On value, the database notes: common and very affordable.
Traditional associations.
In energy work traditions, associated with seeing layers of a situation clearly.
This is lore, and we label it as lore. The measurable facts are further up the page.
Spotting the real thing.
Dark mica that peels into thin flexible glittery sheets with a fingernail.
| Looks like | How to tell them apart |
|---|---|
| Muscovite | Muscovite is silvery-clear; biotite is black-brown |
| Graphite | Graphite is metallic, greasy, and writes on paper |
| Black tourmaline | Tourmaline is hard and never peels into sheets |
At-home tests.
A loupe and a window seat settle most questions about biotite. No workshop required.
| Test | What you should see |
|---|---|
| By eye | Peels into elastic flakes with a fingernail |
| By eye | Flakes spring back when bent |
| By eye | Very soft (Mohs 2.5 to 3) |
Stop short of anything that leaves a mark. A gemologist can answer the rest without damaging the stone.
Care & handling.
At 2.5 to 3 on the Mohs scale this is a soft material. Keep it as a display piece, store it apart from harder stones, and skip daily-wear settings.
It breaks with perfect basal cleavage, peels into flexible sheets, 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 K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂. Crystal system: Monoclinic. Specific gravity: 2.8 to 3.4. Streak: White to gray. Cleavage and fracture: Perfect basal cleavage, peels into flexible sheets.
How it reaches the market
Granites, schists, and gneisses worldwide, one of the most common dark minerals.
What it gets confused with
Muscovite: Muscovite is silvery-clear; biotite is black-brown. Graphite: Graphite is metallic, greasy, and writes on paper. Black tourmaline: Tourmaline is hard and never peels into sheets.
What it is worth
Common and very affordable.
One more thing
The sparkle in many granite countertops is biotite catching the light.
An education-first guide.
We do not carry biotite. 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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