Gearksutite is a rare calcium aluminum fluoride mineral that often forms as chalky, white, earthy masses or crusts. It is typically found in altered cryolite-bearing pegmatites and hydrothermal veins, where it appears as a secondary mineral product of fluorite or cryolite alteration.
Is this gearksutite?
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 gearksutite with a known reference. Gearksutite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: dull.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular, earthy.
Often confused with
Gearksutite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads dull on Gearksutite and pearly to dull earthy on Kaolinite.
How to tell apart: Luster reads dull on Gearksutite and vitreous, pearly on cleavage surfaces, dull in aggregates on Gibbsite.
How to tell apart: Luster reads dull on Gearksutite and vitreous to greasy or waxy, pearly on {001} on Cryolite.
Often found alongside gearksutite
Minerals reported to co-occur with gearksutite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaAl(OH)F₄·H₂O
- Mohs hardness
- 2
- Density
- 2.72-2.768 g/cm³
- Colors
- Streak
- White
- Luster
- Dull
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular, earthy
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In granite and granite pegmatites; may be formed by low-temperature hydrothermal alteration of aluminous rocks by fluorine-bearing hot springs
Where rockhounds find gearksutite
Classic worldwide localities
- Found between Hot Springs and Warm Springs, Bath Co., Virginia, USA
- Chancellor mine, Boulder Co., St. Peters Dome, near Pikes Peak, El Paso Co., and the Wagon Wheel Gap fluorite mine, Mineral Co., Colorado, USA
- Grand Reef mine, Graham Co., Arizona, USA
- Hall mine, near Tonopah, San Antone district, Nye Co., Nevada, USA
- Occurs in the Ivigtut cryolite deposit, southwestern Greenland
- Found near Lake Gjerdingen, Nordmarka, Norway
Field-hunting tip
Where it forms: In granite and granite pegmatites; may be formed by low-temperature hydrothermal alteration of aluminous rocks by fluorine-bearing hot springs. If you start seeing cryolite, thomsenolite, sellaite in float, you are in the right ground. Typical habit: acicular, earthy. Train your eye for that shape before scanning the outcrop.
Common questions
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Is gearksutite safe to handle?+
What rocks look like gearksutite?+
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Find gearksutite on the map
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