Caesiumpharmacosiderite is a rare member of the pharmacosiderite group characterized by the presence of cesium in its structure. It typically occurs as small, sharp, yellow to brownish-yellow cubic crystals in the oxidized crusts of arsenic-rich hydrothermal deposits.
Is this caesiumpharmacosiderite?
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 caesiumpharmacosiderite with a known reference. Caesiumpharmacosiderite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Caesiumpharmacosiderite leaves a yellowish-white streak.
- 3Read the lusterHold the specimen under a strong light. Caesiumpharmacosiderite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, yellowish-brown, greenish-yellow.
- 5Look at form & habitCrystal system: cubic. Typical habit: pseudocubic crystals.
Often confused with
Caesiumpharmacosiderite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Caesiumpharmacosiderite leaves yellowish-white, Pharmacosiderite leaves white; luster reads vitreous on Caesiumpharmacosiderite and adamantine on Pharmacosiderite.
How to tell apart: Scorodite is the harder of the two (Mohs 3.5-4 vs. 2.5); streak differs — Caesiumpharmacosiderite leaves yellowish-white, Scorodite leaves white; luster reads vitreous on Caesiumpharmacosiderite and vitreous to sub-adamantine on Scorodite.
Often found alongside caesiumpharmacosiderite
Minerals reported to co-occur with caesiumpharmacosiderite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CsFe₄(AsO₄)₃(OH)₄·4H₂O
- Mohs hardness
- 2.5
- Density
- 2.9-3.0 g/cm³
- Streak
- Yellowish-white
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Cubic
- Crystal habit
- Pseudocubic Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Arsenic-rich Mineral Deposits
- Typical price
- $50-300 per specimen
Where rockhounds find caesiumpharmacosiderite
Classic worldwide localities
- Czech Republic
- Germany
- United States
Field-hunting tip
Look in oxidized zones of arsenic-rich mineral deposits country — that is the host setting where caesiumpharmacosiderite typically forms. If you start seeing goethite, limonite, arsenopyrite in float, you are in the right ground. Field specimens usually show a pseudocubic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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