Cookeite is a lithium-rich member of the chlorite group that typically forms as a coating or alteration product on other minerals like tourmaline. It is most often found as thin, pearly, micaceous aggregates or soft, pseudo-hexagonal plates in pockets of complex pegmatites.
Is this cookeite?
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 cookeite with a known reference. Cookeite 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. Cookeite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Cookeite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, yellow, pink, green, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: pseudo-hexagonal plates, micaceous, earthy masses.
Often confused with
Cookeite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside cookeite
Minerals reported to co-occur with cookeite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- LiAl₄(Si₃Al)O₁₀(OH)₈
- Mohs hardness
- 2.5-3
- Density
- 2.67 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Pseudo-hexagonal Plates, Micaceous, Earthy Masses
- Cleavage
- Perfect Basal
- Rarity
- Uncommon
- Uses
- Collector, Mineralogical Study
- Host rock
- Lithium-rich Granite Pegmatites
- Typical price
- $10-100 per specimen
Where rockhounds find cookeite
1 mapped spotsClassic worldwide localities
- Mount Mica, Maine, USA
- Himalaya Mine, California, USA
- Mínás Gerais, Brazil
- Nuristan, Afghanistan
- Elba, Italy
Field-hunting tip
Look in lithium-rich granite pegmatites country — that is the host setting where cookeite typically forms. If you start seeing quartz, tourmaline, albite in float, you are in the right ground. Field specimens usually show a pseudo-hexagonal plates, micaceous, earthy masses habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in California — start trip planning there.
Common questions
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Find cookeite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
