Sulphotsumoite is a rare bismuth telluride sulfide that typically appears as metallic, silver-gray foliated masses or lamellar grains. It is most frequently found in hydrothermal gold-bearing deposits and is often visually indistinguishable from other members of the tetradymite group without X-ray diffraction analysis.

Hardness

2.5

Mohs

Luster

Metallic

Streak

Gray

Transparency

Opaque

mineralrareTetradymite Group family

Sulphotsumoite

Hardness: 2.5
Luster: Metallic
Streak: Gray
Transparency: Opaque

Is this sulphotsumoite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch sulphotsumoite with a known reference. Sulphotsumoite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: gray.
3
Read the luster
Hold the specimen under a strong light. Luster: metallic.
4
Match the color range
Compare against the expected color range: gray white.
5
Look at form & habit
Crystal system: trigonal. Typical habit: aggregates, massive.

Often confused with

Sulphotsumoite vs. its common look-alikes, and how to tell them apart in the field.

mineral

Tetradymite

Mohs 1.5-2

How to tell apart: Streak differs, so Sulphotsumoite leaves gray, Tetradymite leaves pale steel-gray.

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Often found alongside sulphotsumoite

Minerals reported to co-occur with sulphotsumoite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: Bi₃Te₂S
Mohs hardness: 2.5
Density: 8.13 g/cm³
Colors: Gray white
Streak: Gray
Luster: Metallic
Transparency: Opaque
Crystal system: Trigonal
Crystal habit: Aggregates, massive
Cleavage: Very perfect in one direction
Rarity: Rare
Uses: Collector
Host rock: Of hydrothermal origin, with other bismuth tellurides

Where rockhounds find sulphotsumoite

Classic worldwide localities

Pogo Au–As–Bi–Te deposit, 145 km east of Fairbanks, Alaska, USA
Burgagylkan Au–Ag deposit, upper Chelomzha River, Magadan district (type locality), and the Egerlyakh deposit, Indigirka River basin, northeastern Sakha (type locality), Russia
Kochbulak gold deposit, Chatkal-Kuramin Mountains, eastern Uzbekistan

Field-hunting tip

Where it forms: Of hydrothermal origin, with other bismuth tellurides. If you start seeing tsumoite, joséite-b in float, you are in the right ground. Typical habit: aggregates, massive. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify sulphotsumoite?+

Mohs hardness is 2.5. Luster: metallic. The streak is gray. Common colors include gray white.

Where is sulphotsumoite found?+

Notable localities include Pogo Au–As–Bi–Te deposit, 145 km east of Fairbanks, Alaska, USA; Burgagylkan Au–Ag deposit, upper Chelomzha River, Magadan district (type locality), and the Egerlyakh deposit, Indigirka River basin, northeastern Sakha (type locality), Russia; Kochbulak gold deposit, Chatkal-Kuramin Mountains, eastern Uzbekistan.

What rocks look like sulphotsumoite?+

Sulphotsumoite is most often confused with Tetradymite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with sulphotsumoite?+

Sulphotsumoite commonly co-occurs with Tsumoite, Joséite-B. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does sulphotsumoite form in?+

Where it forms: Of hydrothermal origin, with other bismuth tellurides. Working float back to the host body is the standard way to chase a fresh occurrence.

What is sulphotsumoite used for?+

Sulphotsumoite is used in collector.

Find sulphotsumoite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.