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?
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 star sapphire with a known reference. Star Sapphire 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. Star Sapphire leaves a none streak.
- 3Read the lusterHold the specimen under a strong light. Star Sapphire typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: blue, gray, violet, black, white.
- 5Look 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.
How to tell apart: Star Sapphire is noticeably harder (Mohs 9 vs. 4.5-7); streak differs — Star Sapphire leaves none, Kyanite leaves white.
How to tell apart: Star Sapphire is noticeably harder (Mohs 9 vs. 6-6.5); streak differs — Star Sapphire leaves none, Benitoite leaves white.
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
- Streak
- None
- 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 — that is 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
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How much is star sapphire worth?+
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Find star sapphire on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
