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Proustite
Proustite is sulfosalts, Ag3AsS3. In the hand, it rates 2 to 2.5 on the Mohs scale, and it runs scarlet vermilion and blood red. Scarlet translucent crystals with diamond-like luster and red streak that slowly darken if displayed in light, the famous 'ruby silver' of old mining camps.
The geology.
Proustite carries the formula Ag3AsS3. It belongs to the trigonal system. On paper it is sulfosalts.
It sits at 2 to 2.5 on the Mohs scale. The surface reads adamantine. Light behaviour is translucent to transparent (darkens in light). Specific gravity runs 5.55 to 5.64. The streak is vermilion red. It breaks with distinct cleavage; conchoidal fracture.
Scarlet translucent crystals with diamond-like luster and red streak that slowly darken if displayed in light, the famous 'ruby silver' of old mining camps.
Expect to see it as prismatic to scalenohedral crystals, crystal sprays or massive ore.
The origins.
Silver vein deposits: Chanarcillo (Chile, historic best), Freiberg and Schneeberg (Germany), Cobalt (Ontario, Canada).
On value, the database notes: premium collector mineral; fine reds are four to five figures.
Traditional associations.
In energy work traditions, associated with transformation and working with hidden inner material.
Recorded here because it is part of how this material is sold, not because it is a property of the material.
Spotting the real thing.
Scarlet translucent crystals with diamond-like luster and red streak that slowly darken if displayed in light, the famous 'ruby silver' of old mining camps.
Rarely faked; light-damaged (blackened) crystals are sometimes oiled to fake freshness.
| Looks like | How to tell them apart |
|---|---|
| Pyrargyrite | Pyrargyrite (dark ruby silver, antimony-based) is deeper red-black; proustite is brighter scarlet |
| Cinnabar | Cinnabar is softer-looking, scarlet too, but SG 8.1 and associated with mercury deposits |
| Cuprite | Cuprite streaks brownish-red metallic and forms octahedra in copper oxide zones |
At-home tests.
None of these need a lab. A 10x loupe, good daylight and a steady hand cover most of what a buyer needs to know about proustite.
| Test | What you should see |
|---|---|
| By eye | Vermilion streak |
| By eye | Very soft (2 to 2.5) and heavy (SG 5.6) |
| By eye | Darkens with light exposure, collectors store it in the dark |
If these checks leave you unsure, that is what appraisers are for. Do not file, heat or soak a piece to find out.
Care & handling.
At 2 to 2.5 on the Mohs scale this is a soft material. Keep it as a display piece, store it apart from harder stones, and skip daily-wear settings.
It breaks with distinct cleavage; conchoidal fracture, which is worth knowing before you set it or drop it.
Most damage happens during cleaning, not wearing. Avoid steamers, ultrasonic tanks and anything from under the sink.
Contains arsenic and silver sulfide: wash hands, no elixirs, store away from light.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is Ag3AsS3. Crystal system: Trigonal. Specific gravity: 5.55 to 5.64. Streak: Vermilion red. Cleavage and fracture: Distinct cleavage; conchoidal fracture.
How it reaches the market
Silver vein deposits: Chanarcillo (Chile, historic best), Freiberg and Schneeberg (Germany), Cobalt (Ontario, Canada).
What it gets confused with
Pyrargyrite: Pyrargyrite (dark ruby silver, antimony-based) is deeper red-black; proustite is brighter scarlet. Cinnabar: Cinnabar is softer-looking, scarlet too, but SG 8.1 and associated with mercury deposits. Cuprite: Cuprite streaks brownish-red metallic and forms octahedra in copper oxide zones.
What it is worth
Premium collector mineral; fine reds are four to five figures.
Where buyers get caught
Rarely faked; light-damaged (blackened) crystals are sometimes oiled to fake freshness.
One more thing
Museum proustites are kept in covered drawers, light literally photo-decomposes the surface; pristine Chilean crystals from the 1800s are crown jewels of silver mineralogy.
An education-first guide.
There is nothing to buy on this page. Proustite is not part of our catalogue, and the guide is here anyway because somebody searching the name deserves a straight answer.
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