Segerstromite is a rare calcium arsenic hydroxide, typically colorless. It is a secondary mineral in a Pb-Ag-As-Cu-Zn deposit hosted in sedimentary and volcanic rocks. It is associated with talmessite and vladimirite. It was first described from Cobriza mine, Sacramento district, Copiapó Province, Atacama Region, Chile.

Hardness

~4.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Segerstromite

Hardness: ~4.5
Luster: Vitreous
Streak: White
Transparency: Transparent

No image

Is this segerstromite?

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 segerstromite with a known reference. Segerstromite sits at Mohs ~4.5, 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: cubic. Typical habit: prismatic crystals.

Often confused with

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

mineral

Mimetite

Mohs 3.5-4

How to tell apart: Luster reads vitreous on Segerstromite and resinous to subadamantine on Mimetite.

How to tell apart: Segerstromite is noticeably harder (Mohs ~4.5 vs. 2.5-3); luster reads vitreous on Segerstromite and adamantine, resinous to vitreous on Anglesite.

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Often found alongside segerstromite

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

All properties

Chemical formula: Ca₃(As⁵⁺O₄)₂[As³⁺(OH)₃]₂
Mohs hardness: ~4.5
Density: 3.44 g/cm³
Colors: Colorless
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Cubic
Crystal habit: Prismatic crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A secondary mineral in a Pb-Ag-As-Cu-Zn deposit hosted in sedimentary and volcanic rocks

Where rockhounds find segerstromite

Classic worldwide localities

Cobriza mine, Sacramento district, Copiapó Province, Atacama Region, Chile

Field-hunting tip

Where it forms: A secondary mineral in a Pb-Ag-As-Cu-Zn deposit hosted in sedimentary and volcanic rocks. If you start seeing talmessite, vladimirite, sr-bearing hydroxylapatite in float, you are in the right ground. Typical habit: prismatic crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify segerstromite?+

Mohs hardness is ~4.5. Luster: vitreous. The streak is white. Common colors include colorless.

Where is segerstromite found?+

Notable localities include Cobriza mine, Sacramento district, Copiapó Province, Atacama Region, Chile.

Is segerstromite safe to handle?+

Segerstromite 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 segerstromite?+

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

What minerals are found with segerstromite?+

Segerstromite commonly co-occurs with Talmessite, Vladimirite, Sr-bearing hydroxylapatite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does segerstromite form in?+

Where it forms: A secondary mineral in a Pb-Ag-As-Cu-Zn deposit hosted in sedimentary and volcanic rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is segerstromite used for?+

Segerstromite is used in collector.

Find segerstromite on the map

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