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

30 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.

Utah9 spots

Field-hunting tip

Look in igneous and metamorphic rocks like granite and schist country, 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, Wisconsin. Start trip planning there.

Browse 30 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 30 biotite rockhounding spots across 12 U.S. states. The top states are Utah, Maine, Wisconsin.

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.