Ferrilotharmeyerite is a rare secondary mineral found in the oxidation zones of arsenic-rich lead-zinc deposits. It typically forms small, attractive yellow to orange tabular crystals and is highly prized by collectors of rare arsenate species.
Is this ferrilotharmeyerite?
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 ferrilotharmeyerite with a known reference. Ferrilotharmeyerite sits at Mohs ~3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: very pale yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine to greasy.
- 4Match the color rangeCompare against the expected color range: brownish yellow, yellow brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: subhedral crystals, tabular, wedge shaped.
Often confused with
Ferrilotharmeyerite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Tsumcorite is the harder of the two (Mohs 4.5 vs. ~3); streak differs, so Ferrilotharmeyerite leaves very pale yellow, Tsumcorite leaves yellow; luster reads adamantine to greasy on Ferrilotharmeyerite and vitreous on Tsumcorite.
How to tell apart: Streak differs, so Ferrilotharmeyerite leaves very pale yellow, Lotharmeyerite leaves pale orange to yellow-orange; luster reads adamantine to greasy on Ferrilotharmeyerite and vitreous on Lotharmeyerite.
How to tell apart: Helmutwinklerite is the harder of the two (Mohs 4.5 vs. ~3); streak differs, so Ferrilotharmeyerite leaves very pale yellow, Helmutwinklerite leaves white; luster reads adamantine to greasy on Ferrilotharmeyerite and vitreous, resinous on fracture surfaces on Helmutwinklerite.
Often found alongside ferrilotharmeyerite
Minerals reported to co-occur with ferrilotharmeyerite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaFe³⁺Zn(AsO₄)₂(OH)·H₂O
- Mohs hardness
- ~3
- Density
- 4.25 g/cm³
- Streak
- Very pale yellow
- Luster
- Adamantine to greasy
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Subhedral crystals, tabular, wedge shaped
- Cleavage
- Good on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Very rare, on museum specimens from a dolostone-hosted hydrothermal polymetallic ore deposit
Where rockhounds find ferrilotharmeyerite
Classic worldwide localities
- Tsumeb, Namibia
Field-hunting tip
Where it forms: Very rare, on museum specimens from a dolostone-hosted hydrothermal polymetallic ore deposit. If you start seeing conichalcite, scorodite, schneiderhöhnite in float, you are in the right ground. Typical habit: subhedral crystals, tabular, wedge shaped. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferrilotharmeyerite?+
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