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.
Is this segerstromite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch segerstromite with a known reference. Segerstromite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Segerstromite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Segerstromite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: cubic. Typical habit: prismatic crystals.
Often confused with
Segerstromite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Mimetite is the harder of the two (Mohs 3.5-4 vs. 2); luster reads vitreous on Segerstromite and resinous to subadamantine on Mimetite.
How to tell apart: Luster reads vitreous on Segerstromite and adamantine on Anglesite.
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
- 2
- Density
- 3.44 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Cubic
- Crystal habit
- Prismatic Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Polymetallic Deposits
Where rockhounds find segerstromite
Classic worldwide localities
- Cobriza mine, Atacama Region, Chile
Field-hunting tip
Look in hydrothermal polymetallic deposits country, the host setting where segerstromite typically forms. If you start seeing tsumebite, leadhillite, cerussite in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find segerstromite on the map
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