Pyroaurite is a member of the hydrotalcite group typically found as pearly, platy crystals or foliated masses in metamorphic environments. It is often distinguished by its characteristic waxy to pearly luster and soft, flexible flakes when found in thin, hexagonal plates.
Is this pyroaurite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch pyroaurite with a known reference. Pyroaurite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: waxy to vitreous, may be pearly.
- 4Match the color rangeCompare against the expected color range: brownish yellow, brown white, colorless, greenish, yellowish white.
- 5Look at form & habitCrystal system: trigonal. Typical habit: fibrous, tabular.
Often confused with
Pyroaurite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside pyroaurite
Minerals reported to co-occur with pyroaurite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₆Fe³⁺₂(CO₃)(OH)₁₆·4H₂O
- Mohs hardness
- 2.5
- Density
- 2.13 g/cm³
- Colors
- Streak
- White
- Luster
- Waxy to vitreous, may be pearly
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Fibrous, tabular
- Cleavage
- Perfect on {0001}
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- In low-temperature hydrothermal veins; in serpentinite and ophiolites; an authigenic weathering product
Where rockhounds find pyroaurite
Classic worldwide localities
- Sterling Hill, Ogdensburg, Sussex Co., New Jersey, USA
- Hunting Hill quarry, Rockville, Montgomery Co., Maryland, USA
- Cedar Hill quarry, Lancaster Co., Pennsylvania, USA
- Gem mine, San Benito Co., California, USA
- Långban and Nordmark, Värmland, Sweden
- Occurs in the Val Malenco, Lombardy, the Val d’Astico, Vicenza, and the Val Ramazzo, Liguria, Italy
Field-hunting tip
Where it forms: In low-temperature hydrothermal veins; in serpentinite and ophiolites; an authigenic weathering product. If you start seeing sjögrenite, calcite, magnesite in float, you are in the right ground. Typical habit: fibrous, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify pyroaurite?+
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What rocks look like pyroaurite?+
What minerals are found with pyroaurite?+
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Find pyroaurite on the map
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