Ottensite is an extremely rare antimony sulfosalt that typically occurs as delicate, hair-like acicular crystals. It is highly sought after by advanced collectors for its striking orange-red color and association with other rare antimony minerals.
Is this ottensite?
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 ottensite with a known reference. Ottensite sits at Mohs 3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellow-brown.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine to vitreous.
- 4Match the color rangeCompare against the expected color range: reddish brown.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: encrustations.
Often confused with
Ottensite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Ottensite is noticeably harder (Mohs 3.5 vs. 2); streak differs, so Ottensite leaves yellow-brown, Stibnite leaves lead-gray; luster reads adamantine to vitreous on Ottensite and metallic, splendent on cleavage surfaces on Stibnite.
How to tell apart: Ottensite is noticeably harder (Mohs 3.5 vs. 1-1.5); streak differs, so Ottensite leaves yellow-brown, Kermesite leaves brownish red.
Often found alongside ottensite
Minerals reported to co-occur with ottensite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₃(Sb₂O₃)₃(SbS₃)·3H₂O
- Mohs hardness
- 3.5
- Density
- 4.14 g/cm³
- Colors
- Streak
- Yellow-brown
- Luster
- Adamantine to vitreous
- Transparency
- Translucent
- Crystal system
- Hexagonal
- Crystal habit
- Encrustations
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A supergene product of stibnite weathering in the oxidation zone
Where rockhounds find ottensite
Classic worldwide localities
- Qinglong mining district, Qinglong County, southwestern Guizhou Province, China and at the Pereta mine, Grosseto Provence, Tuscany, Italy
Field-hunting tip
Where it forms: A supergene product of stibnite weathering in the oxidation zone. If you start seeing stibnite, fluorite, mopungite in float, you are in the right ground. Typical habit: encrustations. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ottensite?+
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Is ottensite safe to handle?+
What rocks look like ottensite?+
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Find ottensite on the map
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