Machatschkiite is a rare calcium arsenate, typically colorless. It is a very rare secondary mineral in crusts on granite. Associated minerals include picropharmacolite, pharmacolite and gypsum. It was first described from Anton mine, Heubachtal, near Schiltach, Black Forest, Germany.
Is this machatschkiite?
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 machatschkiite with a known reference. Machatschkiite sits at Mohs 2-3, 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: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: trigonal. Typical habit: pseudo rhombohedral.
Often confused with
Machatschkiite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Machatschkiite leaves white, Mixite leaves pale bluish green.
How to tell apart: Cornwallite is the harder of the two (Mohs 4.5 vs. 2-3); streak differs, so Machatschkiite leaves white, Cornwallite leaves pale green.
Often found alongside machatschkiite
Minerals reported to co-occur with machatschkiite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₆(AsO₄)(AsO₃OH)₃(PO₄)(H₂O)₁₂·3H₂O
- Mohs hardness
- 2-3
- Density
- 2.5-2.6 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Trigonal
- Crystal habit
- Pseudo rhombohedral
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A very rare secondary mineral in crusts on granite
Where rockhounds find machatschkiite
Classic worldwide localities
- Anton mine, Heubachtal, near Schiltach, Black Forest, Germany
Field-hunting tip
Where it forms: A very rare secondary mineral in crusts on granite. If you start seeing picropharmacolite, pharmacolite, cobaltian sainfeldite in float, you are in the right ground. Typical habit: pseudo rhombohedral. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify machatschkiite?+
Where is machatschkiite found?+
Is machatschkiite safe to handle?+
What rocks look like machatschkiite?+
What minerals are found with machatschkiite?+
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Find machatschkiite on the map
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