Biotite is a common mica mineral known for its dark, plate-like appearance and perfect basal cleavage, which allows it to be peeled into thin, flexible sheets. It is a major constituent of igneous rocks like granite and is frequently found in metamorphic environments like gneiss and schist.

Hardness

2.5-3

Mohs

Luster

Pearly

Streak

White

Transparency

Translucent

mineralcommonMica Group family

Biotite

Hardness: 2.5-3
Luster: Pearly
Streak: White
Transparency: Translucent

Is this biotite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch biotite with a known reference. Biotite sits at Mohs 2.5-3 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Biotite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Biotite typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: black, dark brown, dark green.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals, massive, scaly aggregates.

Often confused with

Biotite vs. its common look-alikes — and how to tell them apart in the field.

Often found alongside biotite

Minerals reported to co-occur with biotite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: K(Mg,Fe)₃(AlSi₃O₁₀)(OH,F)₂
Mohs hardness: 2.5-3
Density: 2.7-3.3 g/cm³
Colors: Black Dark Brown Dark Green
Streak: White
Luster: Pearly
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Tabular Crystals, Massive, Scaly Aggregates
Cleavage: Perfect Basal
Rarity: Common
Uses: Industrial, Collector
Host rock: Igneous and Metamorphic Rocks Like Granite and Schist
Typical price: $2-20 for typical specimens

Where rockhounds find biotite

31 mapped spots

Classic worldwide localities

Norway
Canada
USA
Russia
Greenland

U.S. states with biotite

Each link opens a state-specific list of mapped rockhounding spots that produce biotite.

Field-hunting tip

Look in igneous and metamorphic rocks like granite and schist country — that is the host setting where biotite typically forms. If you start seeing quartz, feldspar, hornblende in float, you are in the right ground. Field specimens usually show a tabular crystals, massive, scaly aggregates habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah, Maine, Georgia — start trip planning there.

Browse 31 U.S. spots for biotite →

Common questions

How do you identify biotite?+

Mohs hardness is 2.5-3. It typically shows a pearly luster. The streak is white. Common colors include black, dark brown, dark green.

Where is biotite found?+

Notable localities include Norway; Canada; USA; Russia; Greenland.

Can I find biotite in the United States?+

RockHoundR maps 31 biotite rockhounding spots across 12 U.S. states — the top states are Utah, Maine, Georgia.

How much is biotite worth?+

Typical asking prices fall in the range of $2-20 for typical specimens. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like biotite?+

Biotite is most often confused with Muscovite, Phlogopite, Chlorite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with biotite?+

Biotite commonly co-occurs with Quartz, Feldspar, Hornblende, Garnet. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does biotite form in?+

Biotite typically forms in igneous and metamorphic rocks like granite and schist. Working float back to the host body is the standard way to chase a fresh occurrence.

What is biotite used for?+

Biotite is used in industrial, collector.

Find biotite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.