Borocookeite is a rare lithium-bearing silicate mineral belonging to the chlorite group, characterized by its inclusion of boron. It typically forms thin, micaceous plates or flaky aggregates within complex granitic pegmatites. Collectors look for it associated with other late-stage pegmatite minerals like tourmaline and albite.
Is this borocookeite?
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 borocookeite with a known reference. Borocookeite sits at Mohs 3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light pinkish gray.
- 3Read the lusterHold the specimen under a strong light. Luster: greasy.
- 4Match the color rangeCompare against the expected color range: light pinkish gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: aggregates, flakes.
Often confused with
Borocookeite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Borocookeite leaves light pinkish gray, Cookeite leaves white; luster reads greasy on Borocookeite and pearly or silky on Cookeite.
How to tell apart: Streak differs, so Borocookeite leaves light pinkish gray, Muscovite leaves white; luster reads greasy on Borocookeite and vitreous to pearly or silky on Muscovite.
How to tell apart: Streak differs, so Borocookeite leaves light pinkish gray, Lepidolite leaves white; luster reads greasy on Borocookeite and pearly to vitreous on Lepidolite.
Often found alongside borocookeite
Minerals reported to co-occur with borocookeite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- LiAl₄(Si₃B)O₁₀(OH)₈
- Mohs hardness
- 3
- Density
- 2.62 g/cm³
- Colors
- Light pinkish gray
- Streak
- Light pinkish gray
- Luster
- Greasy
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Aggregates, flakes
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In miarolitic cavities in gem-bearing, zoned, complex, Li-bearing granitic pegmatite
Where rockhounds find borocookeite
Classic worldwide localities
- Sosedka and Mokhovaya pegmatite veins, Malkhan gem tourmaline deposit, Krasny Chikoy district, Chita oblast, Russia
Field-hunting tip
Where it forms: In miarolitic cavities in gem-bearing, zoned, complex, Li-bearing granitic pegmatite. If you start seeing elbaite, lepidolite, danburite in float, you are in the right ground. Typical habit: aggregates, flakes. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify borocookeite?+
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What rocks look like borocookeite?+
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Find borocookeite on the map
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