Ríosecoite is a rare calcium magnesium arsenite, typically colorless. Associated minerals include camanchacaite, anhydrite and gypsum. It was first described from the Torrecillas mine, Iquique Province, Tarapacá Region, Chile.

Hardness

3.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Ríosecoite

Hardness: 3.5
Luster: Vitreous
Streak: White
Transparency: Transparent

No image

Is this ríosecoite?

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 ríosecoite with a known reference. Ríosecoite sits at Mohs 3.5, 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: colorless.
5
Look at form & habit
Crystal system: triclinic. Typical habit: acicular crystals.

Often confused with

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

mineral

Epsomite

Mohs 2-2.5

How to tell apart: Ríosecoite is noticeably harder (Mohs 3.5 vs. 2-2.5).

How to tell apart: Ríosecoite is noticeably harder (Mohs 3.5 vs. 2-2.5); luster reads vitreous on Ríosecoite and pearly to vitreous on Hexahydrite.

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Often found alongside ríosecoite

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

All properties

Chemical formula: Ca₂Mg(AsO₃OH)₃(H₂O)₂
Mohs hardness: 3.5
Density: 3.24 g/cm³
Colors: Colorless
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Triclinic
Crystal habit: Acicular crystals
Cleavage: Perfect on {001} and {010}
Rarity: Rare
Uses: Collector
Host rock: evaporite deposits

Where rockhounds find ríosecoite

Classic worldwide localities

Torrecillas mine, northern Atacama Desert, Salar Grande, Iquique Province, Tarapacá Region, Chile

Field-hunting tip

Where it forms: evaporite deposits. If you start seeing camanchacaite, anhydrite, gypsum in float, you are in the right ground. Typical habit: acicular crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify ríosecoite?+

Mohs hardness is 3.5. Luster: vitreous. The streak is white. Common colors include colorless.

Where is ríosecoite found?+

Notable localities include Torrecillas mine, northern Atacama Desert, Salar Grande, Iquique Province, Tarapacá Region, Chile.

Is ríosecoite safe to handle?+

Ríosecoite contains arsenic and calls for real care. Contains arsenic, which is toxic if ingested or inhaled as dust. Wash hands thoroughly after handling and avoid creating dust.

What rocks look like ríosecoite?+

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

What minerals are found with ríosecoite?+

Ríosecoite commonly co-occurs with Camanchacaite, Anhydrite, Gypsum, Halite, Talmessite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does ríosecoite form in?+

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

What is ríosecoite used for?+

Ríosecoite is used in collector.

Find ríosecoite on the map

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