Folvikite

folvikite

hausmannite

tenegrenite

jerrygibbsite

Images

Formula: Sb5+Mn3+(Mg,Mn2+)10O8(BO3)4
Borate, oxyborate, pinakiolite group
Specific gravity: 4.14 calculated
Hardness: 6
Streak: Reddish brown
Colour: Black to dark reddish brown
Luminescence: Not fluorescent in UV
Environments

Metamorphic environments

Folkivite was approved in 2016, but to date (June 2022) it has been reported only from the type locality.

Localities

At the type locality, the Kitteln mine, Nordmark Odal Field, Filipstad, Värmland County, Sweden, folvikite is an oxyborate occurring as a primary skarn mineral embedded in calcite. It forms black to dark reddish brown striated prismatic crystals up to 0.3 mm. Associated minerals include hausmannite, tegengrenite, and a magnesium-dominant analogue of sonolite or jerrygibbsite (MM 82.4.821–836).

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