PYROAURITE

Mg₆Fe³⁺₂(CO₃)(OH)₁₆.4H₂O
Hexagonal

	Figure 23-23. Twinned hexagonal platy pyroaurite crystals on acicular crystals of willemite from Sterling Hill. Field of view is 0.4 mm in maximum dimension.

Pyroaurite, a magnesium ferric-iron carbonate hydroxide hydrate mineral, was first discovered from Sterling Hill by Paul Desautels (Frondel, 1972). It has not been found at Franklin. Pyroaurite commonly occurs as light yellow to yellowish-brown, hexagonal, platy crystals, up to several mm in width, and tabular on [0001]. Pyroaurite crystals also occur “sprinkled” and “impaled” on acicular willemite (Figures 23-23 through 23-26).

	Figure 23-24. Abundant platy aggregates of pyroaurite crystals on acicular willemite crystals from Sterling Hill. Field of view is 0.3 mm in maximum dimension.

The luster of pyroaurite is vitreous to dull. No physical or optical data exist. A number of small crystals have been examined semiquantitatively by the writer using microchemical and microprobe methods and were found to be Mg- and Fe³⁺- bearing, with less than 2 wt. % MnO or ZnO.

Pyroaurite is an uncommon mineral locally, occurring on altered vein surfaces, and is associated with willemite, franklinite, calcite, hodgkinsonite, hetaerolite, and other species. In the north orebody, it was found coating hematite and associated with serpentine and calcite. Dunn and Leavens (1981) reported an occurrence on the 1300 level; these specimens consist of willemite-franklinite  ore, with chlorophoenicite, sphalerite, barite, willemite and epitactic sjögrenite as secondary minerals.

	Figure 23-25. Hexagonal pyroaurite crystals with acicular willemite crystals from Sterling Hill. Field of view is 0.2 mm in maximum dimension.		Figure 23-26. Stacked aggregate of pyroaurite crystals from Sterling Hill. Field of view is 0.2 mm in maximum dimension.

Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates
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This page created: January 13, 2001