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, so 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, so 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, 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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