Diaspore is an aluminum oxide hydroxide mineral known for its excellent cleavage and occasional color-changing properties in gem-grade material. It typically forms as platy or acicular crystals within bauxite-rich metamorphic rocks or hydrothermal veins. Collectors prize it for its high luster and the distinct pleochroism exhibited by transparent specimens.
Is this diaspore?
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 diaspore with a known reference. Diaspore sits at Mohs 6.5-7, 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: adamantine, vitreous, pearly on cleavage faces.
- 4Match the color rangeCompare against the expected color range: white, greenish gray, grayish brown, colorless, yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: disseminated, platy, tabular.
Often confused with
Diaspore vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads adamantine, vitreous, pearly on cleavage faces on Diaspore and vitreous to pearly on Kyanite.
How to tell apart: Diaspore is noticeably harder (Mohs 6.5-7 vs. 2.5-3.5); luster reads adamantine, vitreous, pearly on cleavage faces on Diaspore and vitreous, pearly on cleavage surfaces, dull in aggregates on Gibbsite.
How to tell apart: Luster reads adamantine, vitreous, pearly on cleavage faces on Diaspore and vitreous; waxy to dull when massive on Quartz.
Often found alongside diaspore
Minerals reported to co-occur with diaspore. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- AlO(OH)
- Mohs hardness
- 6.5-7
- Density
- 3.2-3.5 g/cm³
- Colors
- Streak
- White
- Luster
- Adamantine, vitreous, pearly on cleavage faces
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Disseminated, platy, tabular
- Cleavage
- {010} perfect, {110} distinct, {100} in traces
- Rarity
- Uncommon
- Uses
- Gemstone, Collector, Industrial
- Host rock
- Typically a final product of diagenesis in bauxite deposits formed by the tropical weathering of alumino-silicate rocks; from hydrothermal alteration of aluminous minerals
Where rockhounds find diaspore
1 mapped spotsClassic worldwide localities
- Chester, Hampden Co., Massachusetts, USA
- Corundum Hill, Newlin, Chester Co., Pennsylvania, USA
- Culsagee, Macon Co., North Carolina, USA
- Swiss, Gasconade Co., Missouri, USA
- Kossoi Brod village, about 37 km south of Yekaterinburg (Sverdlovsk), and Kyshtym, Ural Mountains, Russia
- Banská Belá (Dilln), near Banská Štiavnica (Schemnitz), Slovakia
Field-hunting tip
Where it forms: Typically a final product of diagenesis in bauxite deposits formed by the tropical weathering of alumino-silicate rocks; from hydrothermal alteration of aluminous minerals. If you start seeing corundum, magnetite, margarite in float, you are in the right ground. Typical habit: disseminated, platy, tabular. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Massachusetts. Start trip planning there.
Common questions
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Find diaspore on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
