Achávalite is a rare iron selenide mineral that typically forms as metallic, bronze-colored grains within hydrothermal veins. Collectors most often find it in argentiferous or selenide-bearing mineral deposits where it is usually associated with other rare sulfide and selenide species.
Is this achávalite?
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 achávalite with a known reference. Achávalite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: gray.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: massive, anhedral grains.
Often confused with
Achávalite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Pyrrhotite is the harder of the two (Mohs 3.5-4.5 vs. 2.5); streak differs, so Achávalite leaves black, Pyrrhotite leaves dark grayish black.
How to tell apart: Troilite is the harder of the two (Mohs 3.5-4.5 vs. 2.5); streak differs, so Achávalite leaves black, Troilite leaves dark grayish brown.
Often found alongside achávalite
Minerals reported to co-occur with achávalite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeSe
- Mohs hardness
- 2.5
- Density
- 6.53 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Hexagonal
- Crystal habit
- Massive, anhedral grains
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Same as synthetic delta-Fe7S8 with niccolite structure type
Where rockhounds find achávalite
Classic worldwide localities
- Cerro de Cacheuta, Mendoza, Argentina (type locality)
Field-hunting tip
Where it forms: Same as synthetic delta-Fe7S8 with niccolite structure type. If you start seeing calcite, pyrite, siderite in float, you are in the right ground. Typical habit: massive, anhedral grains. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify achávalite?+
Where is achávalite found?+
Is achávalite safe to handle?+
What rocks look like achávalite?+
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Find achávalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
