Juansilvaite is an extremely rare arsenic-bearing silicate mineral discovered at the Torrecillas mine in Chile. It typically forms thin, platy, bright pink crystal aggregates associated with other rare arsenic-rich species.

Hardness

~2.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Juansilvaite

Hardness: ~2.5
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this juansilvaite?

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 juansilvaite with a known reference. Juansilvaite sits at Mohs ~2.5, 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: bright pink.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: platy crystals, crusts.

Often confused with

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

mineral

Aragonite

Mohs 3.5-4

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

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

Compare →

Often found alongside juansilvaite

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

All properties

Chemical formula: Na₅Al₃[AsO₃(OH)]₄[AsO₂(OH)₂]₂(SO₄)₂·4H₂O
Mohs hardness: ~2.5
Density: 3.01 g/cm³
Colors: Bright pink
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Platy crystals, crusts
Cleavage: Very good on {001}
Rarity: Rare
Uses: Collector
Host rock: From the oxidation of native arsenic and other As-bearing primary phases, followed by later alteration by saline fluids derived from evaporating meteoric water under hyperarid conditions

Where rockhounds find juansilvaite

Classic worldwide localities

Torrecillas mine, northern Atacama Desert, Iquique Province, Chile

Field-hunting tip

Where it forms: From the oxidation of native arsenic and other As-bearing primary phases, followed by later alteration by saline fluids derived from evaporating meteoric water under hyperarid conditions. If you start seeing anhydrite, canutite, halite in float, you are in the right ground. Typical habit: platy crystals, crusts. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify juansilvaite?+

Mohs hardness is ~2.5. Luster: vitreous. The streak is white. Common colors include bright pink.

Where is juansilvaite found?+

Notable localities include Torrecillas mine, northern Atacama Desert, Iquique Province, Chile.

Is juansilvaite safe to handle?+

Juansilvaite contains arsenic and calls for real care. Contains arsenic, a toxic element. Wash hands thoroughly after handling and do not ingest or inhale dust.

What rocks look like juansilvaite?+

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

What minerals are found with juansilvaite?+

Juansilvaite commonly co-occurs with Anhydrite, Canutite, Halite, Sulfur. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does juansilvaite form in?+

Where it forms: From the oxidation of native arsenic and other As-bearing primary phases, followed by later alteration by saline fluids derived from evaporating meteoric water under hyperarid conditions. Working float back to the host body is the standard way to chase a fresh occurrence.

What is juansilvaite used for?+

Juansilvaite is used in collector.

Find juansilvaite on the map

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