Oskarssonite is a rare aluminum fluoride mineral primarily found as a sublimation product in volcanic fumaroles. It typically occurs as small, delicate platy crystals and is often associated with other halide and sulfate minerals in active volcanic environments.

Hardness

1-2

Mohs

Transparency

Translucent

mineralrare

Oskarssonite

Hardness: 1-2
Transparency: Translucent

No image

Is this oskarssonite?

3-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 oskarssonite with a known reference. Oskarssonite sits at Mohs 1-2, softer than the next harder reference, harder than the previous one.
2
Match the color range
Compare against the expected color range: white, grayish yellow.
3
Look at form & habit
Crystal system: trigonal. Typical habit: platy crystals, granular.

Often confused with

Oskarssonite vs. its common look-alikes, and how to tell them apart in the field.

How to tell apart: Chiolite is the harder of the two (Mohs 3.5-4 vs. 1-2).

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Often found alongside oskarssonite

Minerals reported to co-occur with oskarssonite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: AlF₃
Mohs hardness: 1-2
Density: 3.184 g/cm³
Colors: White Grayish yellow
Transparency: Translucent
Crystal system: Trigonal
Crystal habit: Platy crystals, granular
Rarity: Rare
Uses: Collector
Host rock: As sublimate encrustations deposited at 90 °C close to the surface of fumarole vents

Where rockhounds find oskarssonite

Classic worldwide localities

Eldfell volcano, Heimaey Island, Vestmannaeyjar archipelago, Iceland, Antarctica
Reported from Mount Erebus, Antarctica

Field-hunting tip

Where it forms: As sublimate encrustations deposited at 90 °C close to the surface of fumarole vents. If you start seeing anhydrite, bassanite, gypsum in float, you are in the right ground. Typical habit: platy crystals, granular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify oskarssonite?+

Mohs hardness is 1-2. Common colors include white, grayish yellow.

Where is oskarssonite found?+

Notable localities include Eldfell volcano, Heimaey Island, Vestmannaeyjar archipelago, Iceland, Antarctica; Reported from Mount Erebus, Antarctica.

What rocks look like oskarssonite?+

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

What minerals are found with oskarssonite?+

Oskarssonite commonly co-occurs with Anhydrite, Bassanite, Gypsum, Jarosite, Anatase, Hematite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does oskarssonite form in?+

Where it forms: As sublimate encrustations deposited at 90 °C close to the surface of fumarole vents. Working float back to the host body is the standard way to chase a fresh occurrence.

What is oskarssonite used for?+

Oskarssonite is used in collector.

Find oskarssonite on the map

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