Synadelphite is a rare manganese arsenate mineral typically found as reddish-brown prismatic crystals or radial clusters. It is highly valued by mineral collectors for its complexity and association with the unique manganese deposits of Långban, Sweden.
Is this synadelphite?
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 synadelphite with a known reference. Synadelphite 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: yellowish-brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, adamantine to submetallic.
- 4Match the color rangeCompare against the expected color range: colorless, red, reddish brown, dark brown, black.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic, reniform, tabular.
Often confused with
Synadelphite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Synadelphite leaves yellowish-brown, Allactite leaves gray to faint brown.
How to tell apart: Synadelphite is noticeably harder (Mohs 4.5 vs. 3.5); streak differs, so Synadelphite leaves yellowish-brown, Brandtite leaves white.
How to tell apart: Streak differs, so Synadelphite leaves yellowish-brown, Adelite leaves white; luster reads vitreous, adamantine to submetallic on Synadelphite and resinous on Adelite.
Often found alongside synadelphite
Minerals reported to co-occur with synadelphite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn₉(AsO₃)(AsO₄)₂(OH)₉·2H₂O
- Mohs hardness
- 4.5
- Density
- 3.57-3.79 g/cm³
- Streak
- Yellowish-brown
- Luster
- Vitreous, adamantine to submetallic
- Transparency
- Transparent if colorless, grading from translucent to opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic, reniform, tabular
- Cleavage
- On {010}, imperfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare low-temperature hydrothermal mineral cutting hausmannite ores in dolomitic marble (Moss mine, Sweden)
Where rockhounds find synadelphite
Classic worldwide localities
- Sterling Hill, Ogdensburg, Sussex Co., New Jersey, USA
- Found in the Moss mine, Nordmark, and at Långban, Värmland, Sweden
Field-hunting tip
Where it forms: A rare low-temperature hydrothermal mineral cutting hausmannite ores in dolomitic marble (Moss mine, Sweden). If you start seeing pyrochroite, manganite, jacobsite in float, you are in the right ground. Typical habit: prismatic, reniform, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
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What rocks look like synadelphite?+
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Find synadelphite on the map
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