Phlogopite is a magnesium-rich mica commonly found in contact-metamorphosed limestones and ultramafic igneous rocks. It is easily identified by its distinctive brownish color and perfect, flexible micaceous cleavage that allows it to peel into thin, elastic sheets.
Is this phlogopite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch phlogopite with a known reference. Phlogopite sits at Mohs 2.5-3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Phlogopite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Phlogopite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: brown, yellowish-brown, reddish-brown, greenish-brown, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, platy masses, scaly aggregates.
Often confused with
Phlogopite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside phlogopite
Minerals reported to co-occur with phlogopite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KMg₃(AlSi₃O₁₀)(OH)₂
- Mohs hardness
- 2.5-3
- Density
- 2.7-2.9 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular Crystals, Platy Masses, Scaly Aggregates
- Cleavage
- Perfect Basal
- Rarity
- Common
- Uses
- Industrial, Insulation, Collector
- Host rock
- Metamorphosed Limestones and Dolomites, Ultramafic Rocks
- Typical price
- $5-40 for thumbnail to cabinet specimens
Where rockhounds find phlogopite
1 mapped spotsClassic worldwide localities
- Ontario, Canada
- Madagascar
- New York, USA
- Kola Peninsula, Russia
- Tanzania
Field-hunting tip
Look in metamorphosed limestones and dolomites, ultramafic rocks country — that is the host setting where phlogopite typically forms. If you start seeing calcite, dolomite, diopside in float, you are in the right ground. Field specimens usually show a tabular crystals, platy masses, scaly aggregates habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New York — start trip planning there.
Common questions
How do you identify phlogopite?+
Where is phlogopite found?+
Can I find phlogopite in the United States?+
How much is phlogopite worth?+
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Find phlogopite on the map
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