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 4-5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ferrilotharmeyerite leaves a yellowish streak.
- 3Read the lusterHold the specimen under a strong light. Ferrilotharmeyerite typically shows a adamantine luster.
- 4Match the color rangeCompare against the expected color range: yellow, yellowish-orange, brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals.
Often confused with
Ferrilotharmeyerite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Luster reads adamantine on Ferrilotharmeyerite and vitreous on Tsumcorite.
How to tell apart: Streak differs — Ferrilotharmeyerite leaves yellowish, Lotharmeyerite leaves yellow; luster reads adamantine on Ferrilotharmeyerite and vitreous on Lotharmeyerite.
How to tell apart: Ferrilotharmeyerite is noticeably harder (Mohs 4-5 vs. 2); streak differs — Ferrilotharmeyerite leaves yellowish, Helmutwinklerite leaves yellow; luster reads adamantine on Ferrilotharmeyerite and vitreous 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
- 4-5
- Density
- 4.56 g/cm³
- Streak
- Yellowish
- Luster
- Adamantine
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Hydrothermal Lead-zinc Deposits
- Typical price
- $50-500 depending on specimen size and quality
Where rockhounds find ferrilotharmeyerite
Classic worldwide localities
- Tsumeb Mine (Namibia)
- Ojuela Mine (Mexico)
Field-hunting tip
Look in oxidized hydrothermal lead-zinc deposits country — that is the host setting where ferrilotharmeyerite typically forms. If you start seeing arsenates, calcite, galena in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find ferrilotharmeyerite on the map
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