Arangasite is a rare aluminum phosphate mineral typically found as small crusts or fibrous aggregates. It is most easily identified by its occurrence in specific phosphate-rich geological environments where it often forms alongside other secondary phosphate minerals.
Is this arangasite?
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 arangasite with a known reference. Arangasite sits at Mohs 1-2, 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 to silky.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, massive, crusts.
Often confused with
Arangasite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Wavellite is the harder of the two (Mohs 3.5-4 vs. 1-2); luster reads dull to silky on Arangasite and vitreous to resinous, pearly on Wavellite.
How to tell apart: Variscite is the harder of the two (Mohs 4.5 vs. 1-2); luster reads dull to silky on Arangasite and vitreous to waxy on Variscite.
Often found alongside arangasite
Minerals reported to co-occur with arangasite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₂(SO₄)(PO₄)F·9H₂O
- Mohs hardness
- 1-2
- Density
- 2.01 g/cm³
- Colors
- Streak
- White
- Luster
- Dull to silky
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, massive, crusts
- Cleavage
- Imperfect basal
- Rarity
- Rare
- Uses
- Collector
- Host rock
- phosphate-bearing sedimentary deposits
Where rockhounds find arangasite
Classic worldwide localities
- Alyaskitovy cassiterite-silicate-sulfide deposit, lower reaches of Arangas Creek, a tributary of the Elga River, Indigirka River basin, eastern Sakha (Yakutia), Russia
Field-hunting tip
Where it forms: phosphate-bearing sedimentary deposits. If you start seeing phosphorscorodite, fluellite, gypsum in float, you are in the right ground. Typical habit: fibrous, massive, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify arangasite?+
Where is arangasite found?+
What rocks look like arangasite?+
What minerals are found with arangasite?+
What kind of rock does arangasite form in?+
What is arangasite used for?+
Find arangasite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
