Formula: Ca5(AsO4)3(OH)
Anhydrous arsenate containing hydroxyl, apatite group
Specific gravity: 3.68
Hardness: 4½
Streak: White
Colour: Light greyish white

Metamorphic environments

Johnbaumite occurs in skarn, commonly associated with biotite and calcite (Mindat).


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 96.5.402).

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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