Jakobssonite is an extremely rare aluminum fluoride mineral known primarily from the Ivigtut cryolite deposit in Greenland. It typically forms as small, colorless tabular crystals associated with other rare fluoride minerals in hydrothermal environments. Collectors prize it as a significant mineralogical rarity from classic pegmatite localities.
Is this jakobssonite?
4-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 jakobssonite with a known reference. Jakobssonite sits at Mohs 3.5, softer than the next harder reference, harder than the previous one.
- 2Read the lusterHold the specimen under a strong light. Luster: earthy.
- 3Match the color rangeCompare against the expected color range: white.
- 4Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals.
Often confused with
Jakobssonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Jakobssonite is noticeably harder (Mohs 3.5 vs. 2.5); luster reads earthy on Jakobssonite and vitreous to greasy or waxy, pearly on {001} on Cryolite.
How to tell apart: Luster reads earthy on Jakobssonite and vitreous, pearly on the basal cleavage on Chiolite.
Often found alongside jakobssonite
Minerals reported to co-occur with jakobssonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaAlF₅
- Mohs hardness
- 3.5
- Density
- 2.89 g/cm³
- Colors
- Luster
- Earthy
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Forms crusts around fumaroles in active basaltic volcanoes
Where rockhounds find jakobssonite
Classic worldwide localities
- Eldfell volcano, Heimaey Island, and Hekla volcano, Iceland
Field-hunting tip
Where it forms: Forms crusts around fumaroles in active basaltic volcanoes. If you start seeing ralstonite, gypsum, hematite in float, you are in the right ground. Typical habit: tabular crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify jakobssonite?+
Where is jakobssonite found?+
What rocks look like jakobssonite?+
What minerals are found with jakobssonite?+
What kind of rock does jakobssonite form in?+
What is jakobssonite used for?+
Find jakobssonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
