Star Ruby is a variety of Corundum that exhibits asterism, a star-like optical effect caused by the reflection of light off needle-like rutile inclusions. Collectors should look for a well-centered, sharp six-rayed star that moves across the surface of a polished cabochon. High-quality specimens are typically found in gem-gravel deposits and metamorphic marble formations.
Is this star ruby?
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 ruby with a known reference. Star Ruby 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 Ruby leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Star Ruby typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: red, purplish-red, pinkish-red.
- 5Look at form & habitCrystal system: trigonal. Typical habit: hexagonal bipyramidal crystals with characteristic silky inclusions.
Often confused with
Star Ruby vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Star Ruby is noticeably harder (Mohs 9 vs. 6.5-7.5).
How to tell apart: Star Ruby is noticeably harder (Mohs 9 vs. 8).
How to tell apart: Star Ruby is noticeably harder (Mohs 9 vs. 7-7.5).
Often found alongside star ruby
Minerals reported to co-occur with star ruby. 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
- 3.99-4.10 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Hexagonal Bipyramidal Crystals with Characteristic Silky Inclusions
- Cleavage
- None
- Fluorescence
- Strong Red Under UV
- Rarity
- Rare
- Uses
- Gemstone, Collector
- Host rock
- Metamorphic Rocks Such as Marble and Schist
- Typical price
- $100-5000+ per carat depending on quality and star sharpness
Where rockhounds find star ruby
Classic worldwide localities
- Myanmar
- Sri Lanka
- Thailand
- Vietnam
- India
Field-hunting tip
Look in metamorphic rocks such as marble and schist country — that is the host setting where star ruby typically forms. If you start seeing calcite, feldspar, mica in float, you are in the right ground. Field specimens usually show a hexagonal bipyramidal crystals with characteristic silky inclusions habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find star ruby on the map
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