Picaite is an extremely rare selenite mineral found in the arid nitrate-rich environments of Chile. It typically forms small, clear, tabular crystals in association with other evaporite minerals.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Picaite

Picaite is an extremely rare selenite mineral found in the arid nitrate-rich environments of Chile. It typically forms small, clear, tabular crystals in association with other evaporite minerals.

Hardness: 2
Luster: Vitreous
Streak: White
Transparency: Transparent

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Is this picaite?

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 picaite with a known reference. Picaite 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: vitreous.
4
Match the color range
Compare against the expected color range: colorless, white.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals.

Often confused with

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

mineral

Gypsum

Mohs 1.5-2

How to tell apart: Luster reads vitreous on Picaite and subvitreous, pearly on {010} cleavages, silky if fibrous on Gypsum.

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Often found alongside picaite

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

All properties

Chemical formula: NaCa[AsO₃OH][AsO₂(OH)₂]
Mohs hardness: 2
Colors: Colorless White
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular crystals
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: nitrate deposits

Where rockhounds find picaite

Classic worldwide localities

Pampa del Tamarugal, Tarapacá Region, Chile

Field-hunting tip

Where it forms: nitrate deposits. If you start seeing halite, nitratine, probertite in float, you are in the right ground. Typical habit: tabular crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify picaite?+

Mohs hardness is 2. Luster: vitreous. The streak is white. Common colors include colorless, white.

Where is picaite found?+

Notable localities include Pampa del Tamarugal, Tarapacá Region, Chile.

Is picaite safe to handle?+

Picaite contains arsenic and calls for real care. Picaite contains selenium, which is toxic; always wash hands after handling and avoid inhaling dust.

What rocks look like picaite?+

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

What minerals are found with picaite?+

Picaite commonly co-occurs with halite, nitratine, probertite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does picaite form in?+

Where it forms: nitrate deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is picaite used for?+

Picaite is used in collector.

Find picaite on the map

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