Alarsite is an extremely rare aluminum arsenate mineral discovered in the fumaroles of the Tolbachik volcano. It typically occurs as small, clear, tabular to rhombohedral crystals forming on volcanic rocks and is chemically related to the phosphate mineral berlinite.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Semitransparent

mineralrare

Alarsite

Hardness: 3
Luster: Vitreous
Streak: White
Transparency: Semitransparent

Is this alarsite?

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 alarsite with a known reference. Alarsite sits at Mohs 3, 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: vitreous.
4
Match the color range
Compare against the expected color range: colorless, yellowish, pale green, bluish.
5
Look at form & habit
Crystal system: trigonal. Typical habit: anhedral grains, encrustations.

Often confused with

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

mineral

Berlinite

Mohs ~6.5

How to tell apart: Berlinite is the harder of the two (Mohs ~6.5 vs. 3).

Compare →

Often found alongside alarsite

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

All properties

Chemical formula: AlAsO₄
Mohs hardness: 3
Density: 3.32 g/cm³
Colors: Colorless Yellowish Pale green Bluish
Streak: White
Luster: Vitreous
Transparency: Semitransparent
Crystal system: Trigonal
Crystal habit: Anhedral grains, encrustations
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A fumarolic mineral

Where rockhounds find alarsite

Classic worldwide localities

Occurs at the Tolbachik fissure volcano, Kamchatka Peninsula, Russia

Field-hunting tip

Where it forms: A fumarolic mineral. If you start seeing fedotovite, klyuchevskite, lammerite in float, you are in the right ground. Typical habit: anhedral grains, encrustations. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify alarsite?+

Mohs hardness is 3. Luster: vitreous. The streak is white. Common colors include colorless, yellowish, pale green, bluish.

Where is alarsite found?+

Notable localities include Occurs at the Tolbachik fissure volcano, Kamchatka Peninsula, Russia.

Is alarsite safe to handle?+

Alarsite contains arsenic and calls for real care. Contains arsenic, which is toxic. Handle with caution, avoid ingestion, inhalation of dust, or skin contact, and wash hands thoroughly after handling.

What rocks look like alarsite?+

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

What minerals are found with alarsite?+

Alarsite commonly co-occurs with Fedotovite, Klyuchevskite, Lammerite, Nabokoite, Atlasovite, Langbeinite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does alarsite form in?+

Where it forms: A fumarolic mineral. Working float back to the host body is the standard way to chase a fresh occurrence.

What is alarsite used for?+

Alarsite is used in collector.

Find alarsite on the map

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