Jahnsite-(CaMnMg)

jahnsite-(CaMnMg)

leucophosphite

hureaulite

collinsite

Images

Formula: CaMn2+Mg2Fe3+2(PO4)4(OH)2.8H2O
Hydrated phosphate containing hydroxyl, jahnsite subgroup, jahnsite group, manganese-bearing mineral
Crystal System: Monoclinic
Specific gravity: 2.706 to 2.718 measured,  2.715 calculated
Hardness: 4
Streak: White
Colour: Brown, golden brown, purplish brown, yellow, yellow-orange, greenish yellow
Luminescence: Not fluorescent under UV
Solubility: Soluble in dilute hydrochloric acid
Environments

Pegmatites

Jahnsite-(CaMnMg) occurs in granitic pegmatites.

Localities

At the type locality, the Tip Top mine, Fourmile, Custer Mining District, Custer county, South Dakota, USA, jahnsite-(CaMnMg) occurs as a late stage product in corroded triphylite - heterosite - ferrisicklerite - rockbridgeite masses. Associated minerals include leucophosphite, hureaulite, collinsite, laueite, vivianite, triphylite, tavorite, rockbridgeite and robertsite.
The jahnsite-(CaMnMg) forms tabular short to long prismatic crystals with vitreous to subadamantine lustre of a nut-brown, purplish brown, yellow, yellow-orange, or greenish yellow colour. Persistent striations parallel to the prism distinguish it from hureaulite and leucophosphite (AM 59.48-59, Mindat).

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