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 3-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Allactite leaves a light brown streak.
- 3Read the lusterHold the specimen under a strong light. Allactite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dark red, reddish brown, brown.
- 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: Iron Ore is the harder of the two (Mohs 5-6.5 vs. 3-4); streak differs — Allactite leaves light brown, Iron Ore leaves reddish-brown to black; luster reads vitreous on Allactite and metallic to submetallic on Iron Ore.
How to tell apart: Garnet is the harder of the two (Mohs 6.5-7.5 vs. 3-4); streak differs — Allactite leaves light 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
- 3-4
- Density
- 3.84 g/cm³
- Streak
- Light Brown
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic to Tabular Crystals, Sometimes in Radiating Sprays or as Crusts
- Cleavage
- Distinct On {110}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphosed Manganese Ore Deposits
- Typical price
- $50-500 thumbnail
Where rockhounds find allactite
Classic worldwide localities
- Långban, Värmland, Sweden
- Nordmark, Värmland, Sweden
- Franklin, New Jersey, USA
Field-hunting tip
Look in metamorphosed manganese ore deposits country — that is the host setting where allactite typically forms. If you start seeing hausmannite, barite, calcite in float, you are in the right ground. Field specimens usually show a prismatic to tabular crystals, sometimes in radiating sprays or as crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find allactite on the map
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