Star Sapphire is a variety of Corundum that displays an optical phenomenon known as asterism, where a six-rayed star appears on the surface when viewed under a direct light source. This effect is caused by tiny, needle-like inclusions of rutile aligned in multiple directions within the crystal lattice. Collectors should look for a centered, sharp star that moves smoothly across the cabochon-cut dome.
Is this star sapphire?
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 star sapphire with a known reference. Star Sapphire sits at Mohs 9, softer than the next harder reference, harder than the previous one.
- 2Read the lusterHold the specimen under a strong light. Star Sapphire typically shows a vitreous luster.
- 3Match the color rangeCompare against the expected color range: blue, gray, violet, black, white.
- 4Look at form & habitCrystal system: trigonal. Typical habit: hexagonal prisms.
Often confused with
Star Sapphire vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside star sapphire
Minerals reported to co-occur with star sapphire. 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
- 3.98-4.1 g/cm³
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Hexagonal Prisms
- Cleavage
- None
- Rarity
- Rare
- Uses
- Gemstone, Collector
- Host rock
- Metamorphic Rocks
- Typical price
- $100-5000+ depending on star quality, color intensity, and weight
Where rockhounds find star sapphire
Classic worldwide localities
- Sri Lanka
- Myanmar
- Madagascar
- Thailand
- Tanzania
Field-hunting tip
Look in metamorphic rocks country, the host setting where star sapphire typically forms. If you start seeing zircon, rutile, spinel in float, you are in the right ground. Field specimens usually show a hexagonal prisms habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify star sapphire?+
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How much is star sapphire worth?+
What rocks look like star sapphire?+
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Find star sapphire on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
