Thalliumpharmacosiderite is a rare member of the pharmacosiderite group characterized by the inclusion of thallium in its chemical structure. It typically presents as small, yellow to yellowish-green cubic or pseudocubic crystals found in the oxidized zones of arsenic-rich mineral deposits. Due to its toxicity and rarity, it is sought primarily by advanced mineral collectors specializing in rare species or rare-element minerals.
Is this thalliumpharmacosiderite?
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 thalliumpharmacosiderite with a known reference. Thalliumpharmacosiderite 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. Thalliumpharmacosiderite leaves a yellowish-white streak.
- 3Read the lusterHold the specimen under a strong light. Thalliumpharmacosiderite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, yellowish-green, brown.
- 5Look at form & habitCrystal system: cubic. Typical habit: pseudocubic crystals, massive.
Often confused with
Thalliumpharmacosiderite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Thalliumpharmacosiderite leaves yellowish-white, Pharmacosiderite leaves white; luster reads vitreous on Thalliumpharmacosiderite and adamantine on Pharmacosiderite.
How to tell apart: Scorodite is the harder of the two (Mohs 3.5-4 vs. 2.5); streak differs — Thalliumpharmacosiderite leaves yellowish-white, Scorodite leaves white; luster reads vitreous on Thalliumpharmacosiderite and vitreous to sub-adamantine on Scorodite.
Often found alongside thalliumpharmacosiderite
Minerals reported to co-occur with thalliumpharmacosiderite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- TlFe₄(AsO₄)₃(OH)₄·4H₂O
- Mohs hardness
- 2.5
- Density
- 3.5 g/cm³
- Streak
- Yellowish-white
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Cubic
- Crystal habit
- Pseudocubic Crystals, Massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Arsenic-rich Hydrothermal Deposits
- Typical price
- $50-300 per specimen
Where rockhounds find thalliumpharmacosiderite
Classic worldwide localities
- Jas Roux, France
- Gold Hill, Utah, USA
- Cap Garonne, France
Field-hunting tip
Look in oxidized arsenic-rich hydrothermal deposits country — that is the host setting where thalliumpharmacosiderite typically forms. If you start seeing pharmacosiderite, arsenopyrite, goethite in float, you are in the right ground. Field specimens usually show a pseudocubic crystals, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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