Katiarsite is an extremely rare copper arsenate mineral discovered in the fumaroles of the Tolbachik volcano in Russia. It typically appears as white, acicular crystal aggregates and crusts associated with volcanic exhalations. Due to its very restricted type locality, it is highly prized by advanced mineral collectors of rare species.

Hardness

2.5

Mohs

Luster

Vitreous

Transparency

Transparent

mineralrare

Katiarsite

Hardness: 2.5
Luster: Vitreous
Transparency: Transparent

No image

Is this katiarsite?

4-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 katiarsite with a known reference. Katiarsite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
2
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
3
Match the color range
Compare against the expected color range: colorless.
4
Look at form & habit
Crystal system: orthorhombic. Typical habit: crusts, aggregates of small acicular crystals.

Often confused with

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

mineral

Euchroite

Mohs 3.5-4

How to tell apart: Euchroite is the harder of the two (Mohs 3.5-4 vs. 2.5).

Often found alongside katiarsite

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

All properties

Chemical formula: KTiO(AsO₄)
Mohs hardness: 2.5
Density: 3.49 g/cm³
Colors: Colorless
Luster: Vitreous
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Crusts, aggregates of small acicular crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Formed in sublimates encrusting basaltic scoria around a volcanic fumarole

Where rockhounds find katiarsite

Classic worldwide localities

Arsenatnaya fumarole, Second scoria cone, Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia

Field-hunting tip

Where it forms: Formed in sublimates encrusting basaltic scoria around a volcanic fumarole. If you start seeing hatertite, bradaczekite, johillerite in float, you are in the right ground. Typical habit: crusts, aggregates of small acicular crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify katiarsite?+

Mohs hardness is 2.5. Luster: vitreous. Common colors include colorless.

Where is katiarsite found?+

Notable localities include Arsenatnaya fumarole, Second scoria cone, Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia.

Is katiarsite safe to handle?+

Katiarsite contains arsenic and calls for real care. Contains arsenic and copper; avoid ingestion, inhalation of dust, and wash hands thoroughly after handling specimens.

What rocks look like katiarsite?+

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

What minerals are found with katiarsite?+

Katiarsite commonly co-occurs with Hatertite, Bradaczekite, Johillerite, Yurmarinite, Tilasite, Arsmirandite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does katiarsite form in?+

Where it forms: Formed in sublimates encrusting basaltic scoria around a volcanic fumarole. Working float back to the host body is the standard way to chase a fresh occurrence.

What is katiarsite used for?+

Katiarsite is used in collector.

Find katiarsite on the map

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