Natropharmacosiderite is a rare secondary mineral found in the oxidation zones of arsenic-bearing ore deposits. It typically forms small, sharp, bright green cubic crystals that are prized by mineral collectors for their vibrant color and geometric perfection.
Is this natropharmacosiderite?
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 natropharmacosiderite with a known reference. Natropharmacosiderite 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. Natropharmacosiderite leaves a pale yellow streak.
- 3Read the lusterHold the specimen under a strong light. Natropharmacosiderite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: green, yellow-green, olive-green.
- 5Look at form & habitCrystal system: cubic. Typical habit: cubes, sometimes with truncated corners.
Often confused with
Natropharmacosiderite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Natropharmacosiderite leaves pale yellow, Pharmacosiderite leaves white; luster reads vitreous on Natropharmacosiderite and adamantine on Pharmacosiderite.
How to tell apart: Scorodite is the harder of the two (Mohs 3.5-4 vs. 2.5); streak differs — Natropharmacosiderite leaves pale yellow, Scorodite leaves white; luster reads vitreous on Natropharmacosiderite and vitreous to sub-adamantine on Scorodite.
Often found alongside natropharmacosiderite
Minerals reported to co-occur with natropharmacosiderite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaFe₃(AsO₄)₂(OH)₄·4H₂O
- Mohs hardness
- 2.5
- Density
- 2.7-2.8 g/cm³
- Streak
- Pale Yellow
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Cubic
- Crystal habit
- Cubes, Sometimes with Truncated Corners
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Arsenic-rich Hydrothermal Deposits
- Typical price
- $20-150 for small specimens
Where rockhounds find natropharmacosiderite
Classic worldwide localities
- Cornwall, England
- Germany
- Chile
- United States
Field-hunting tip
Look in oxidized zones of arsenic-rich hydrothermal deposits country — that is the host setting where natropharmacosiderite typically forms. If you start seeing arsenopyrite, limonite, scorodite in float, you are in the right ground. Field specimens usually show a cubes, sometimes with truncated corners habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find natropharmacosiderite on the map
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