Brassite is a rare magnesium arsenate mineral that typically forms as delicate crusts or small tabular crystals in the oxidation zones of arsenic-bearing ore deposits. Due to its solubility and rarity, it is primarily sought after by advanced mineral collectors who specialize in arsenate species.

Hardness

Mohs

Luster

Pearly

Streak

White

Transparency

Semitransparent

mineralrare

Brassite

Hardness: 2
Luster: Pearly
Streak: White
Transparency: Semitransparent

Is this brassite?

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 brassite with a known reference. Brassite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: pearly.
4
Match the color range
Compare against the expected color range: white.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: crusts, tabular crystals.

Often confused with

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

mineral

Newberyite

Mohs 3-3.5

How to tell apart: Newberyite is the harder of the two (Mohs 3-3.5 vs. 2); luster reads pearly on Brassite and vitreous on Newberyite.

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Often found alongside brassite

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

All properties

Chemical formula: MgHAsO₄·4H₂O
Mohs hardness: 2
Density: 2.28 g/cm³
Colors: White
Streak: White
Luster: Pearly
Transparency: Semitransparent
Crystal system: Orthorhombic
Crystal habit: Crusts, tabular crystals
Cleavage: Perfect on {001}
Rarity: Rare
Uses: Collector
Host rock: A rare reaction product of arsenic-rich solutions with Ca–Mg carbonates

Where rockhounds find brassite

Classic worldwide localities

Jáchymov (Joachimsthal), Czech Republic
Bieber and Richelsdorf, Hesse, and Wittichen, Black Forest, Germany
Ruben mine, Kohlendorf, Nowa Ruda (Neurode), Silesia, Poland
Salsigne mine, 15 km north of Carcassone, Aude, France

Field-hunting tip

Where it forms: A rare reaction product of arsenic-rich solutions with Ca–Mg carbonates. If you start seeing pharmacolite, picropharmacolite, weilite in float, you are in the right ground. Typical habit: crusts, tabular crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify brassite?+

Mohs hardness is 2. Luster: pearly. The streak is white. Common colors include white.

Where is brassite found?+

Notable localities include Jáchymov (Joachimsthal), Czech Republic; Bieber and Richelsdorf, Hesse, and Wittichen, Black Forest, Germany; Ruben mine, Kohlendorf, Nowa Ruda (Neurode), Silesia, Poland; Salsigne mine, 15 km north of Carcassone, Aude, France.

Is brassite safe to handle?+

Brassite contains arsenic and calls for real care. Contains arsenic, a toxic element. Handle with care, avoid inhalation of dust, and wash hands thoroughly after handling specimens.

What rocks look like brassite?+

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

What minerals are found with brassite?+

Brassite commonly co-occurs with Pharmacolite, Picropharmacolite, Weilite, Haidingerite, Rauenthalite, Arsenic. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does brassite form in?+

Where it forms: A rare reaction product of arsenic-rich solutions with Ca–Mg carbonates. Working float back to the host body is the standard way to chase a fresh occurrence.

What is brassite used for?+

Brassite is used in collector.

Find brassite on the map

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