Césarferreiraite is a rare hydrated iron arsenate mineral typically found as small, yellow, prismatic crystals in oxidized zones of arsenic-bearing pegmatites. It is often discovered as radial clusters associated with other secondary arsenic minerals like scorodite. Collectors should handle it with care due to its arsenic content.
Is this césarferreiraite?
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 césarferreiraite with a known reference. Césarferreiraite 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. Césarferreiraite leaves a pale to greenish yellow streak.
- 3Read the lusterHold the specimen under a strong light. Césarferreiraite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, yellow-brown.
- 5Look at form & habitCrystal system: triclinic. Typical habit: prismatic crystals, radial aggregates.
Often confused with
Césarferreiraite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Scorodite is the harder of the two (Mohs 3.5-4 vs. 2); streak differs, so Césarferreiraite leaves pale to greenish yellow, Scorodite leaves white; luster reads vitreous on Césarferreiraite and vitreous to subadamantine on Scorodite.
How to tell apart: Streak differs, so Césarferreiraite leaves pale to greenish yellow, Pharmacosiderite leaves yellowish green; luster reads vitreous on Césarferreiraite and adamantine on Pharmacosiderite.
Often found alongside césarferreiraite
Minerals reported to co-occur with césarferreiraite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe²⁺Fe³⁺₂(AsO₄)₂F₂·8H₂O
- Mohs hardness
- 2
- Density
- 2.93 g/cm³
- Colors
- Streak
- Pale to Greenish Yellow
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Prismatic Crystals, Radial Aggregates
- Cleavage
- Distinct On {010} and {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Granite Pegmatites
Where rockhounds find césarferreiraite
Classic worldwide localities
- Lavra do Cigano, Minas Gerais, Brazil
Field-hunting tip
Look in granite pegmatites country, the host setting where césarferreiraite typically forms. If you start seeing arsenopyrite, löllingite, quartz in float, you are in the right ground. Field specimens usually show a prismatic crystals, radial aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify césarferreiraite?+
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Find césarferreiraite on the map
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