Mcalpineite is a rare copper tellurate mineral typically found as tiny green to yellow-green grains within oxidized gold-telluride ore deposits. It is primarily a collector's mineral and is rarely seen in crystals, usually appearing as encrustations or granular masses in association with other tellurium minerals.
Is this mcalpineite?
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 mcalpineite with a known reference. Mcalpineite sits at Mohs 3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: paler green.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine.
- 4Match the color rangeCompare against the expected color range: emerald green, olive green, dark greenish black.
- 5Look at form & habitCrystal system: cubic. Typical habit: encrustations.
Often confused with
Mcalpineite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Mcalpineite is noticeably harder (Mohs 3 vs. 2); streak differs, so Mcalpineite leaves paler green, Tellurite leaves white; luster reads adamantine on Mcalpineite and subadamantine on Tellurite.
How to tell apart: Emmonsite is the harder of the two (Mohs ~5 vs. 3); streak differs, so Mcalpineite leaves paler green, Emmonsite leaves pale yellow; luster reads adamantine on Mcalpineite and vitreous on Emmonsite.
Often found alongside mcalpineite
Minerals reported to co-occur with mcalpineite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₃TeO₆
- Mohs hardness
- 3
- Density
- 6.63 g/cm³
- Colors
- Streak
- Paler green
- Luster
- Adamantine
- Transparency
- Translucent to transparent
- Crystal system
- Cubic
- Crystal habit
- Encrustations
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A very rare secondary mineral, formed by alteration of tellurides and tellurium-bearing sulfides
Where rockhounds find mcalpineite
Classic worldwide localities
- McAlpine mine, Tuolumne Co., California, and at the Centennial Eureka mine, Tintic district, Juab Co., Utah, USA
- Gambatesa mine, Val Graveglia, eastern Liguria, Italy
Field-hunting tip
Where it forms: A very rare secondary mineral, formed by alteration of tellurides and tellurium-bearing sulfides. If you start seeing quartz, chromian muscovite, choloalite in float, you are in the right ground. Typical habit: encrustations. Train your eye for that shape before scanning the outcrop.
Common questions
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What rocks look like mcalpineite?+
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Find mcalpineite on the map
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