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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine.
- 4Match the color rangeCompare against the expected color range: brown, yellowish brown, dark brown.
- 5Look at form & habitCrystal system: triclinic. Typical habit: spherical, tabular.
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, so Gerdtremmelite leaves white, Ludlockite leaves pale brown; luster reads adamantine on Gerdtremmelite and subadamantine on Ludlockite.
How to tell apart: Legrandite is the harder of the two (Mohs 4.5 vs. 3); luster reads adamantine on Gerdtremmelite and vitreous on Legrandite.
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
- ZnAl₂AsO₄(OH)₅
- Mohs hardness
- 3
- Density
- 3.66 g/cm³
- Streak
- White
- Luster
- Adamantine
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Spherical, tabular
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A very rare secondary mineral from the deep oxidized zone of a dolostone-hosted hydrothermal polymetallic ore deposit
Where rockhounds find gerdtremmelite
Classic worldwide localities
- Tsumeb, Namibia
Field-hunting tip
Where it forms: A very rare secondary mineral from the deep oxidized zone of a dolostone-hosted hydrothermal polymetallic ore deposit. If you start seeing powellite, betpakdalite, scorodite in float, you are in the right ground. Typical habit: spherical, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gerdtremmelite?+
Where is gerdtremmelite found?+
Is gerdtremmelite safe to handle?+
What rocks look like gerdtremmelite?+
What minerals are found with gerdtremmelite?+
What kind of rock does gerdtremmelite form in?+
What is gerdtremmelite used for?+
Find gerdtremmelite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
