Gerdtremmelite is an extremely rare arsenate mineral known primarily from the Tsumeb Mine in Namibia. It typically forms as small, yellow, tabular crystals and is highly sought after by advanced collectors of secondary mineral species.
Is this gerdtremmelite?
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 gerdtremmelite with a known reference. Gerdtremmelite 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. Gerdtremmelite leaves a yellowish-white streak.
- 3Read the lusterHold the specimen under a strong light. Gerdtremmelite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, brownish-yellow.
- 5Look at form & habitCrystal system: triclinic. Typical habit: tabular crystals.
Often confused with
Gerdtremmelite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Gerdtremmelite is noticeably harder (Mohs 3 vs. 1.5-2); streak differs — Gerdtremmelite leaves yellowish-white, Ludlockite leaves yellow-orange; luster reads vitreous on Gerdtremmelite and resinous on Ludlockite.
How to tell apart: Legrandite is the harder of the two (Mohs 4.5 vs. 3); streak differs — Gerdtremmelite leaves yellowish-white, Legrandite leaves white.
Often found alongside gerdtremmelite
Minerals reported to co-occur with gerdtremmelite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Zn₂Fe³⁺₃(AsO₄)(OH)₈
- Mohs hardness
- 3
- Density
- 4.21 g/cm³
- Colors
- Streak
- Yellowish-white
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Tabular Crystals
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Polymetallic Ore Deposits
- Typical price
- $200-800 per specimen depending on size and quality
Where rockhounds find gerdtremmelite
Classic worldwide localities
- Tsumeb Mine, Namibia
Field-hunting tip
Look in hydrothermal polymetallic ore deposits country — that is the host setting where gerdtremmelite typically forms. If you start seeing tsumcorite, schultenite, willemite 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 gerdtremmelite on the map
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