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, 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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