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

3-4

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Alarsite

Hardness: 3-4
Luster: Vitreous
Streak: White
Transparency: Transparent

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 3-4 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Alarsite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Alarsite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: white, colorless.
5
Look at form & habit
Crystal system: trigonal. Typical habit: tabular to rhombohedral crystals.

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. 3-4).

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: 3-4
Density: 2.98 g/cm³
Colors: White Colorless
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Trigonal
Crystal habit: Tabular to Rhombohedral Crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Fumaroles of Volcanic Craters
Typical price: $100-500+ depending on crystal size and specimen quality

Where rockhounds find alarsite

Classic worldwide localities

Tolbachik volcano, Kamchatka Peninsula, Russia

Field-hunting tip

Look in fumaroles of volcanic craters country — that is the host setting where alarsite typically forms. If you start seeing hematite, tenorite, orthoclase in float, you are in the right ground. Field specimens usually show a tabular to rhombohedral crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify alarsite?+

Mohs hardness is 3-4. It typically shows a vitreous luster. The streak is white. Common colors include white, colorless.

Where is alarsite found?+

Notable localities include Tolbachik volcano, Kamchatka Peninsula, Russia.

How much is alarsite worth?+

Typical asking prices fall in the range of $100-500+ depending on crystal size and specimen quality. Quality, size, and provenance can move individual specimens well outside that range.

Is alarsite safe to handle?+

It contains toxic constituents. Contains arsenic, which is toxic. Handle with caution, avoid ingestion, inhalation of dust, or skin contact, and wash hands thoroughly after handling. Handle with care, avoid grinding or breathing dust, and store separately.

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 Hematite, Tenorite, Orthoclase. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does alarsite form in?+

Alarsite typically forms in fumaroles of volcanic craters. 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.