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Formula: Ca5(AsO4)3(OH)
Anhydrous arsenate containing hydroxyl,
apatite group
Specific gravity: 3.68
Hardness: 4½
Streak: White
Colour: Light greyish white
Environments:
Johnbaumite occurs in skarn, commonly associated with
biotite and calcite
(Mindat).
Localities
At the Shijiang Shan-Shalonggou mining area, Inner Mongolia, China, the mineral deposits occur predominantly in
veins of hydrothermal origin in skarn. Johnbaumite appears principally
as white crystals to 12 mm long. One exceptional specimen shows intersecting prisms of johnbaumite about 4 cm
long and 2 cm in cross-section, mostly obscured by a coating of small dogtooth
calcite crystals with adhering crystals of microscopic
apophyllite. Johnbaumite is associated with
sphalerite, roweite,
olshanskyite, andradite, and
sometimes wurtzite. Johnbaumite is the second
arsenic-bearing secondary
mineral from the Shijiangshan skarn, the other being
cahnite. The arsenic probably
originates from arsenopyrite
(R&M 96.5.401).
At the Långban mine, Långban Ore District, Filipstad, Värmland County, Sweden, johnbaumite is associated with
tilasite, andradite,
calcite and caryopilite
(HOM).
The type locality is the Franklin Mine, Franklin, Franklin Mining District, Sussex County, New Jersey, USA. Here johnbaumite
occurs in metamorphic zinc-bearing skarn, associated with
zincite, yeatmanite,
roméite, franklinite,
diopside, copper,
calcite and andradite
(Mindat, HOM). Johnbaumite is the massive matrix host for yeatmanite,
which occurs in apparent chemical equilibrium with johnbaumite. Johnbaumite is also host to
diopside, andradite,
franklinite, copper and
roméite. There are indications that diopside was
the first phase to form; it is rimmed by andradite with inclusions of
roméite in the andradite
(AM 65.1143-1145).
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