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, 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
How do you identify cookeite?+
Where is cookeite found?+
Can I find cookeite in the United States?+
How much is cookeite worth?+
What rocks look like cookeite?+
What minerals are found with cookeite?+
What kind of rock does cookeite form in?+
What is cookeite used for?+
Find cookeite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
