Blue Corundum is popularly known as sapphire, prized for its exceptional hardness and rich blue color caused by titanium and iron impurities. It typically forms as hexagonal, barrel-shaped crystals and is most often recovered from alluvial deposits or metamorphic rocks like marble and gneiss.
Is this blue corundum?
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 blue corundum with a known reference. Blue Corundum sits at Mohs 9, softer than the next harder reference, harder than the previous one.
- 2Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 3Match the color rangeCompare against the expected color range: blue, violet-blue, greenish-blue.
- 4Look at form & habitCrystal system: trigonal. Typical habit: hexagonal bipyramidal or barrel-shaped crystals.
Often confused with
Blue Corundum vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Blue Corundum is noticeably harder (Mohs 9 vs. 6-6.5).
How to tell apart: Blue Corundum is noticeably harder (Mohs 9 vs. 5.5-7).
How to tell apart: Blue Corundum is noticeably harder (Mohs 9 vs. 6.5-7).
Often found alongside blue corundum
Minerals reported to co-occur with blue corundum. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₂O₃
- Mohs hardness
- 9
- Density
- 3.95-4.10 g/cm³
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Hexagonal bipyramidal or barrel-shaped crystals
- Cleavage
- None, parting common
- Rarity
- Uncommon
- Uses
- Gemstone, Collector, Jewelry
- Host rock
- pegmatites, marble, and alluvial gravels
Where rockhounds find blue corundum
4 mapped spotsClassic worldwide localities
- Sri Lanka
- Myanmar
- Madagascar
- Kashmir
- Montana, USA
Field-hunting tip
Where it forms: pegmatites, marble, and alluvial gravels. If you start seeing zircon, spinel, garnet in float, you are in the right ground. Typical habit: hexagonal bipyramidal or barrel-shaped crystals. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New York, North Carolina, Pennsylvania. Start trip planning there.
More blue corundum photos
Common questions
How do you identify blue corundum?+
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Can I find blue corundum in the United States?+
What rocks look like blue corundum?+
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Find blue corundum on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
