Dimorphite is a rare arsenic sulfide mineral found primarily in volcanic fumaroles as small, bright orange to yellow crystals. It is chemically unstable and tends to alter into realgar or other arsenic sulfides when exposed to light and air for extended periods.

Hardness

1.5

Mohs

Luster

Resinous

Streak

Yellow

Transparency

Translucent

mineralrare

Dimorphite

Hardness: 1.5
Luster: Resinous
Streak: Yellow
Transparency: Translucent

Is this dimorphite?

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 dimorphite with a known reference. Dimorphite sits at Mohs 1.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Dimorphite leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Dimorphite typically shows a resinous luster.
4
Match the color range
Compare against the expected color range: orange, yellow.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: tabular crystals, crusts, radial aggregates.

Often confused with

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

mineral

Realgar

Mohs 1.5-2

How to tell apart: Streak differs — Dimorphite leaves yellow, Realgar leaves orange-red.

Often found alongside dimorphite

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

All properties

Chemical formula: As₄S₃
Mohs hardness: 1.5
Density: 2.5-2.6 g/cm³
Colors: Orange Yellow
Streak: Yellow
Luster: Resinous
Transparency: Translucent
Crystal system: Orthorhombic
Crystal habit: Tabular Crystals, Crusts, Radial Aggregates
Cleavage: Perfect
Rarity: Rare
Uses: Collector, Scientific Research
Host rock: Fumarolic Deposits in Volcanic Environments
Typical price: $50-300 per specimen

Where rockhounds find dimorphite

Classic worldwide localities

Solfatara di Pozzuoli, Italy
Vulcano, Italy

Field-hunting tip

Look in fumarolic deposits in volcanic environments country — that is the host setting where dimorphite typically forms. If you start seeing realgar, orpiment, sulfur in float, you are in the right ground. Field specimens usually show a tabular crystals, crusts, radial aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify dimorphite?+

Mohs hardness is 1.5. It typically shows a resinous luster. The streak is yellow. Common colors include orange, yellow.

Where is dimorphite found?+

Notable localities include Solfatara di Pozzuoli, Italy; Vulcano, Italy.

How much is dimorphite worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is dimorphite safe to handle?+

It contains toxic constituents. Contains arsenic, which is highly toxic if ingested or inhaled as dust. Handle with extreme care and wash hands thoroughly after contact. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like dimorphite?+

Dimorphite is most often confused with Realgar, Orpiment. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with dimorphite?+

Dimorphite commonly co-occurs with Realgar, Orpiment, Sulfur, Gypsum. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does dimorphite form in?+

Dimorphite typically forms in fumarolic deposits in volcanic environments. Working float back to the host body is the standard way to chase a fresh occurrence.

What is dimorphite used for?+

Dimorphite is used in collector, scientific research.

Find dimorphite on the map

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