Mgriite is an extremely rare copper iron arsenic selenide mineral usually found as microscopic grains. It is primarily identified through laboratory analysis and is most famously associated with the unique selenium-rich mineralogy found at Hope's Nose in England.
Is this mgriite?
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 mgriite with a known reference. Mgriite sits at Mohs 4.5-5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: brownish gray, light gray.
- 5Look at form & habitCrystal system: cubic. Typical habit: massive.
Often confused with
Mgriite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Mgriite is noticeably harder (Mohs 4.5-5 vs. 2-2.5); streak differs, so Mgriite leaves black, Tengchongite leaves light yellow; luster reads metallic on Mgriite and vitreous on Tengchongite.
How to tell apart: Mgriite is noticeably harder (Mohs 4.5-5 vs. 2-2.5).
Often found alongside mgriite
Minerals reported to co-occur with mgriite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₃AsSe₃
- Mohs hardness
- 4.5-5
- Density
- 4.9 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In hydrothermal veins
Where rockhounds find mgriite
Classic worldwide localities
- Erzgibirge, Saxony, Germany (type locality)
Field-hunting tip
Where it forms: In hydrothermal veins. If you start seeing clausthalite, berzelianite, umangite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.
Common questions
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Find mgriite on the map
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