Oxide containing hydroxyl, paramorph of groutite and manganite
Specific gravity: 3.249 calculated
Colour: Lead-grey, brownish black
Feitknechtite is a supergene mineral that typically forms intergrowths with
hausmannite (MW). It is formed by
supergene oxidation and replacement of earlier
pyrochroite. Associated minerals include pyrochroite
At Långban, Filipstad, Värmland County, Sweden, feitknechtite occurs in altered pyrochroite (Dana).
At the Benallt Mine, Rhiw, Aberdaron, Gwynedd, Wales, UK, feitknechtite has been discovered as a component of bladed manganese ore, as coarse brown bladed crystals consisting of an intimate mixture of hausmannite and feitknechtite, typical of what was once termed "hydrohausmannite". This ore is believed to have originally consisted of pyrochroite which altered on exposure to air (MW).
At the type locality, the Franklin mine, Franklin, Franklin Mining District, Sussex County, New Jersey, USA, feitknechtite occurs as an alteration product of pyrochroite, and lining solution cavities in an matrix of calcite, sussexite and zincite (Dana). Associated minerals include pyrochroite and hausmannite (Mindat).
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