Allactite is a rare manganese arsenate mineral prized by collectors for its deep, rich red color and distinctive prismatic crystal forms. It is primarily found in the metamorphosed manganese-rich deposits of Sweden, often occurring as small, well-defined crystals on matrix.
Is this allactite?
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 allactite with a known reference. Allactite sits at Mohs 4.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: gray to faint brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, slightly greasy on fracture surfaces.
- 4Match the color rangeCompare against the expected color range: brown red, greenish brown, purple red, pink.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic to tabular crystals, sometimes in radiating sprays or as crusts.
Often confused with
Allactite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Allactite leaves gray to faint brown, Hematite leaves cherry-red or reddish brown; luster reads vitreous, slightly greasy on fracture surfaces on Allactite and metallic or submetallic to dull on Hematite.
How to tell apart: Garnet is the harder of the two (Mohs 6.5-7.5 vs. 4.5); streak differs, so Allactite leaves gray to faint brown, Garnet leaves white.
Often found alongside allactite
Minerals reported to co-occur with allactite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn₇(AsO₄)₂(OH)₈
- Mohs hardness
- 4.5
- Density
- 3.83 g/cm³
- Streak
- Gray to faint brown
- Luster
- Vitreous, slightly greasy on fracture surfaces
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic to tabular crystals, sometimes in radiating sprays or as crusts
- Cleavage
- Distinct, {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- As a rare secondary mineral in veinlets through metamorphosed manganese deposits (Sweden); in a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA)
Where rockhounds find allactite
Classic worldwide localities
- Franklin and Sterling Hill, Ogdensburg, Sussex Co., New Jersey, USA
- Moss and Brattfors mines, Nordmark, and at Långban, Värmland, Sweden
Field-hunting tip
Where it forms: As a rare secondary mineral in veinlets through metamorphosed manganese deposits (Sweden); in a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA). If you start seeing synadelphite, hematolite, hausmannite in float, you are in the right ground. Typical habit: prismatic to tabular crystals, sometimes in radiating sprays or as crusts. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify allactite?+
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Find allactite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
