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?
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 blue corundum with a known reference. Blue Corundum sits at Mohs 9 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Blue Corundum leaves a none streak.
- 3Read the lusterHold the specimen under a strong light. Blue Corundum typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: blue, violet-blue, greenish-blue.
- 5Look 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); streak differs — Blue Corundum leaves none, Benitoite leaves white.
How to tell apart: Blue Corundum is noticeably harder (Mohs 9 vs. 4.5-7); streak differs — Blue Corundum leaves none, Kyanite leaves white.
How to tell apart: Blue Corundum is noticeably harder (Mohs 9 vs. 6.5-7); streak differs — Blue Corundum leaves none, Tanzanite leaves white.
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
- Streak
- None
- 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
- Typical price
- $50-500 per carat for average stones, $1000+ per carat for fine unheated material
Where rockhounds find blue corundum
3 mapped spotsClassic worldwide localities
- Sri Lanka
- Myanmar
- Madagascar
- Kashmir
- Montana, USA
Field-hunting tip
Look in pegmatites, marble, and alluvial gravels country — that is the host setting where blue corundum typically forms. If you start seeing zircon, spinel, garnet in float, you are in the right ground. Field specimens usually show a hexagonal bipyramidal or barrel-shaped crystals habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New York, Pennsylvania, Washington — start trip planning there.
Common questions
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Find blue corundum on the map
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