Nickeltalmessite is a rare nickel-dominant arsenate belonging to the fairfieldite group, typically found as attractive green crystalline coatings or small sprays. Collectors prize it for its bright color and association with other rare secondary arsenate minerals in oxidized ore zones.
Is this nickeltalmessite?
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 nickeltalmessite with a known reference. Nickeltalmessite sits at Mohs ~4, 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: vitreous.
- 4Match the color rangeCompare against the expected color range: apple green.
- 5Look at form & habitCrystal system: triclinic. Typical habit: bladed, drusy crusts, spherulitic aggregates.
Often confused with
Nickeltalmessite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Talmessite is the harder of the two (Mohs 5 vs. ~4).
How to tell apart: Streak differs, so Nickeltalmessite leaves white, Roselite leaves light red.
How to tell apart: Gaitite is the harder of the two (Mohs ~5 vs. ~4).
Often found alongside nickeltalmessite
Minerals reported to co-occur with nickeltalmessite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂Ni(AsO₄)₂·2H₂O
- Mohs hardness
- ~4
- Density
- 3.72 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Bladed, drusy crusts, spherulitic aggregates
- Cleavage
- Perfect on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Secondary in the weathered zone of a hydrothermal arsenopyrite-glaucodot-cobaltite deposit
Where rockhounds find nickeltalmessite
Classic worldwide localities
- Aїt Ahmane mine, Bou Azzer ore district, central Anti-Atlas, Morocco
Field-hunting tip
Where it forms: Secondary in the weathered zone of a hydrothermal arsenopyrite-glaucodot-cobaltite deposit. If you start seeing annabergite, nickelaustinite, pecoraite in float, you are in the right ground. Typical habit: bladed, drusy crusts, spherulitic aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify nickeltalmessite?+
Where is nickeltalmessite found?+
Is nickeltalmessite safe to handle?+
What rocks look like nickeltalmessite?+
What minerals are found with nickeltalmessite?+
What kind of rock does nickeltalmessite form in?+
What is nickeltalmessite used for?+
Find nickeltalmessite on the map
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