Melanarsite is a rare copper-iron arsenate mineral found primarily in the fumarolic environments of volcanic regions. It typically appears as small, dark, tabular crystals associated with other secondary arsenic minerals. Collectors prize it for its extreme rarity and specific occurrence within volcanic vent systems.
Is this melanarsite?
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 melanarsite with a known reference. Melanarsite 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: dark green with an olive hue.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals.
Often confused with
Melanarsite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Melanarsite is noticeably harder (Mohs ~4 vs. 2.5-3); streak differs, so Melanarsite leaves dark green with an olive hue, Clinoclase leaves bluish green.
How to tell apart: Melanarsite is noticeably harder (Mohs ~4 vs. 3); streak differs, so Melanarsite leaves dark green with an olive hue, Olivenite leaves olive-green to brown; luster reads vitreous on Melanarsite and adamantine to vitreous, pearly to silky if fibrous on Olivenite.
Often found alongside melanarsite
Minerals reported to co-occur with melanarsite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₃Cu₇FeO₄(AsO₄)₄
- Mohs hardness
- ~4
- Density
- 4.386 g/cm³
- Colors
- Streak
- Dark green with an olive hue
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- As sublimates on scoria around an active fumarole
Where rockhounds find melanarsite
Classic worldwide localities
- Arsenatnaya fumarole, Second scoria cone, Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia
Field-hunting tip
Where it forms: As sublimates on scoria around an active fumarole. If you start seeing dmisokolovite, shchurovskite, bradaczekite in float, you are in the right ground. Typical habit: tabular crystals. Train your eye for that shape before scanning the outcrop.
Common questions
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Find melanarsite on the map
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