Muthmannite is a rare silver-gold telluride often found in epithermal gold deposits. It is typically identified in massive form within hydrothermal quartz veins, characterized by its metallic luster and high density.
Is this muthmannite?
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 muthmannite with a known reference. Muthmannite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black to gray-black.
- 3Read the lusterHold the specimen under a strong light. Luster: bright metallic.
- 4Match the color rangeCompare against the expected color range: blackish yellow, bronzy yellow, grayish white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive, tabular.
Often confused with
Muthmannite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Muthmannite leaves black to gray-black, Sylvanite leaves steel-gray to silver-white; luster reads bright metallic on Muthmannite and metallic, brilliant on Sylvanite.
How to tell apart: Streak differs, so Muthmannite leaves black to gray-black, Calaverite leaves greenish to yellowish gray; luster reads bright metallic on Muthmannite and metallic on Calaverite.
How to tell apart: Streak differs, so Muthmannite leaves black to gray-black, Petzite leaves grayish black; luster reads bright metallic on Muthmannite and metallic on Petzite.
Often found alongside muthmannite
Minerals reported to co-occur with muthmannite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- AgAuTe₂
- Mohs hardness
- 2.5
- Density
- 11.04 g/cm³
- Colors
- Streak
- Black to gray-black
- Luster
- Bright metallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Massive, tabular
- Cleavage
- One perfect, in zone of elongation
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In close intergrowths with other tellurides, especially krennerite, in epithermal hydrothermal veins, and in ores enriched by secondary processes (Săcărı̂mb, Romania); replacing calaverite (Baia-de-Arieş, Romania)
Where rockhounds find muthmannite
Classic worldwide localities
- Romania, from Săcărı̂mb (Nagyág) (type locality) and Baia-de-Arieş (Offenbánya)
Field-hunting tip
Where it forms: In close intergrowths with other tellurides, especially krennerite, in epithermal hydrothermal veins, and in ores enriched by secondary processes (Săcărı̂mb, Romania); replacing calaverite (Baia-de-Arieş, Romania). If you start seeing krennerite, stibnite, hessite in float, you are in the right ground. Typical habit: massive, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
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Find muthmannite on the map
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