Synadelphite Locality: Moss mine, Nordmark, Filipstad, Värmland, Sweden Picture width 2 mm. Collection and photograph Christian Rewitzer — Photo: Christian Rewitzer · CC BY-SA 3.0
Synadelphite
Synadelphite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Mn²⁺₉(AsO₄)₂(AsO₃)(OH)₉·2H₂O.
It crystallizes in the orthorhombic crystal system (space group Pnma).
Key properties: Mohs hardness 4.5; specific gravity 3.57–3.79; Vitreous, adamantine to submetallic luster; optically biaxial.
IMA symbol Syd, grandfathered status — known before the IMA’s founding, named in 1884.
A rare low-temperature hydrothermal mineral cutting hausmannite ores in dolomitic marble (Moss mine, Sweden).
It is found associated with Pyrochroite, manganite, jacobsite, allactite, calcite (Moss mine, Sweden); manganon biotite, allactite, hausmannite (Långban, Sweden); kraisslite.
Its name comes from the Greek for with and brother, as it is commonly associated with several other chemically similar minerals.