Keystoneite is an extremely rare copper tellurite mineral typically found as delicate blue crusts or drusy coatings. It is primarily identified in oxidized zones of gold-telluride ore deposits and requires magnification to appreciate its crystal form.
Is this keystoneite?
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 keystoneite with a known reference. Keystoneite sits at Mohs 2-3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Keystoneite leaves a light blue streak.
- 3Read the lusterHold the specimen under a strong light. Keystoneite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: blue, greenish blue.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: microcrystalline crusts, drusy coatings.
Often confused with
Keystoneite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside keystoneite
Minerals reported to co-occur with keystoneite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₃TeO₆·2H₂O
- Mohs hardness
- 2-3
- Density
- 3.85 g/cm³
- Colors
- Streak
- Light Blue
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Microcrystalline Crusts, Drusy Coatings
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Tellurium-bearing Hydrothermal Gold Veins
- Typical price
- $100-500+ per specimen depending on size and rarity
Where rockhounds find keystoneite
Classic worldwide localities
- Keystone Mine, Colorado, USA
- Goldfield, Nevada, USA
Field-hunting tip
Look in tellurium-bearing hydrothermal gold veins country — that is the host setting where keystoneite typically forms. If you start seeing tellurium, coloradoite, quartz in float, you are in the right ground. Field specimens usually show a microcrystalline crusts, drusy coatings habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find keystoneite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
