Sarmientite is a very rare secondary iron arsenate mineral found in the oxidized zones of arsenic-rich ore deposits. It typically forms attractive acicular or fibrous clusters that are easily recognized by their vibrant yellow to orange-yellow color.
Is this sarmientite?
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 sarmientite with a known reference. Sarmientite sits at Mohs 3.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Sarmientite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Sarmientite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, orange-yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular crystals, fibrous, crusts.
Often confused with
Sarmientite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Luster reads vitreous on Sarmientite and vitreous to sub-adamantine on Scorodite.
How to tell apart: Sarmientite is noticeably harder (Mohs 3.5 vs. 2.5); luster reads vitreous on Sarmientite and adamantine on Pharmacosiderite.
Often found alongside sarmientite
Minerals reported to co-occur with sarmientite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₂⁺²(AsO₄)(OH)·5H₂O
- Mohs hardness
- 3.5
- Density
- 3.6 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular Crystals, Fibrous, Crusts
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Arsenic-rich Hydrothermal Deposits
- Typical price
- $50-300 for micro/thumbnail specimens
Where rockhounds find sarmientite
Classic worldwide localities
- Cachiyuyo de Llampos, Chile
- Gold Hill, Utah, USA
Field-hunting tip
Look in oxidized arsenic-rich hydrothermal deposits country — that is the host setting where sarmientite typically forms. If you start seeing arsenopyrite, limonite, jarosite in float, you are in the right ground. Field specimens usually show a acicular crystals, fibrous, crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify sarmientite?+
Where is sarmientite found?+
How much is sarmientite worth?+
Is sarmientite safe to handle?+
What rocks look like sarmientite?+
What minerals are found with sarmientite?+
What kind of rock does sarmientite form in?+
What is sarmientite used for?+
Find sarmientite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
