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.

Hardness

2-3

Mohs

Luster

Dull

Streak

White

Transparency

Opaque

mineralrare

Gearksutite

Hardness: 2-3
Luster: Dull
Streak: White
Transparency: Opaque

Is this gearksutite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch gearksutite with a known reference. Gearksutite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Gearksutite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Gearksutite typically shows a dull luster.
4
Match the color range
Compare against the expected color range: white, colorless, grayish.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: massive, chalky, earthy, botryoidal, or powdery crusts.

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 vitreous on Gibbsite.

How to tell apart: Luster reads dull on Gearksutite and vitreous to greasy on Cryolite.

Compare →

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: 2-3
Density: 2.7-2.8 g/cm³
Colors: White Colorless Grayish
Streak: White
Luster: Dull
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Massive, Chalky, Earthy, Botryoidal, Or Powdery Crusts
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Granite Pegmatites, Hydrothermal Deposits

Where rockhounds find gearksutite

Classic worldwide localities

Greenland
Colorado, USA
Kazakhstan
Tajikistan

Field-hunting tip

Look in granite pegmatites, hydrothermal deposits country, the host setting where gearksutite typically forms. If you start seeing cryolite, fluorite, siderite in float, you are in the right ground. Field specimens usually show a massive, chalky, earthy, botryoidal, or powdery crusts habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify gearksutite?+

Mohs hardness is 2-3. It typically shows a dull luster. The streak is white. Common colors include white, colorless, grayish.

Where is gearksutite found?+

Notable localities include Greenland; Colorado, USA; Kazakhstan; Tajikistan.

Is gearksutite safe to handle?+

It contains toxic constituents. Contains fluorine; handle with care and avoid inhalation of dust or ingestion. Wash hands thoroughly after handling specimens. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like gearksutite?+

Gearksutite is most often confused with Kaolinite, Gibbsite, Cryolite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with gearksutite?+

Gearksutite commonly co-occurs with Cryolite, Fluorite, Siderite, Quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does gearksutite form in?+

Gearksutite typically forms in granite pegmatites, hydrothermal deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is gearksutite used for?+

Gearksutite is used in collector.

Find gearksutite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.