THE MINERAL PYROAURITE

Chemistry: Mg₆Fe₂CO₃(OH)₁₆ - 4H₂O, Hydrated Magnesium Iron Carbonate Hydroxide.
Class: Carbonate.
Group: Hydrotalcite.
Uses: Only as mineral specimens.
Specimens

Pyroaurite is a rare mineral that comes mostly from the famous mines of Langban, Varmland, Sweden, but is also found at a few other localities. It forms platy to tabular crystals. Crystals of pyroaurite can yield flashes of yellow and it is this display that is responsible for its name; which loosely translated means golden fire. Pyroaurite is dimorphous with the mineral sjogrenite. Dimorphs are minerals that share the same chemistry but have different structures.

PHYSICAL CHARACTERISTICS:

Color is usually brownish yellow, reddish brown, yellow, white and greenish brown.
Luster is vitreous to pearly.
Transparency: Crystals are usually translucent to transparent.
Crystal System is trigonal; bar 3 2/m.
Crystal Habits include tabular, scaley to platy crystals; also found in fibrous forms.
Cleavage is perfect in one direction (basal).
Hardness is 2.5.
Specific Gravity is 2.1 (very light).
Streak is white.
Associated Minerals includes hydromagnesite, stitchite, calcite, reevesite, sjogrenite, magnetite and lizardite.
Notable Occurrences include the type locality of Langban, Varmland, Sweden; Gulsen Quarry, Kraubath, Styria, Austria; Tunnel Hill Quarry, Tasmania, Australia; Sterling Hill, New Jersey; San Francisco County, California, USA; Half-Grunay, Shetland Islands, Scotland; Rutherglan, Ontario and the Parker Mine, Notre Dame du Laus, Quebec, Canada.
Best Field Indicators are crystal habits, cleavage, color and locality.

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PYROAURITE specimens:
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PYROAURITE specimen pya-1
$ 25.00

Dims: 1.22x0.67x0.71" (3.1x1.7x1.8 cm)

Wt: 0.41 oz. (11.7g)

Langban, Varmland, Sweden

This pyroaurite specimen is from its type locality (Langban). It is perhaps 50% pyroaurite by weight, with most of the rest being calcite and a metal sulfide that I can't identify for certain (it is shiny and almost black, and the only crystal fragment I can see under a loupe looks a lot like magnetite). The pyroaurite is a thick band of an off-white mass of tiny, platy, transparent crystals that have a fairly distinctive reflection pattern under a loupe. The calcite base is noticeably whiter, reflects light differently, and (most distictively) fluoresces a bright orange under short-wave ultraviolet light.

pya-1 ($ 25.00)

Langban, Varmland, Sweden