Orthopinakiolite is a rare borate mineral primarily found in high-grade manganese skarn deposits. It typically forms dark, submetallic, elongated prismatic crystals that can be difficult to distinguish from related borates without mineralogical analysis.
Is this orthopinakiolite?
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 orthopinakiolite with a known reference. Orthopinakiolite sits at Mohs 6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brown gray.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals, elongated, fibrous to acicular aggregates.
Often confused with
Orthopinakiolite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Orthopinakiolite leaves brown gray, Pinakiolite leaves brownish gray.
How to tell apart: Streak differs, so Orthopinakiolite leaves brown gray, Ludwigite leaves black to greenish black; luster reads metallic on Orthopinakiolite and submetallic on Ludwigite.
Often found alongside orthopinakiolite
Minerals reported to co-occur with orthopinakiolite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Mg,Mn²⁺)₃Mn³⁺(BO₃)O₂
- Mohs hardness
- 6
- Density
- 3.935-4.03 g/cm³
- Colors
- Streak
- Brown gray
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic crystals, elongated, fibrous to acicular aggregates
- Cleavage
- Good on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A very rare species formed in veinlets in granular dolomite in a metamorphosed Fe–Mn orebody
Where rockhounds find orthopinakiolite
Classic worldwide localities
- Långban, Värmland, Sweden
Field-hunting tip
Where it forms: A very rare species formed in veinlets in granular dolomite in a metamorphosed Fe–Mn orebody. If you start seeing hausmannite, manganophyllite, dolomite in float, you are in the right ground. Typical habit: prismatic crystals, elongated, fibrous to acicular aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify orthopinakiolite?+
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What rocks look like orthopinakiolite?+
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Find orthopinakiolite on the map
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