Coquandite is a rare secondary antimony sulfate mineral typically found as small, brilliant, yellow to colorless tabular crystals. It most commonly occurs in oxidized zones of antimony-rich hydrothermal deposits, often associated with other antimony oxides. Collectors prize it for its high luster and complex crystal habits, though it is usually found only as small specimens.
Is this coquandite?
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 coquandite with a known reference. Coquandite sits at Mohs 3-4, 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: adamantine to pearly.
- 4Match the color rangeCompare against the expected color range: colorless, white.
- 5Look at form & habitCrystal system: triclinic. Typical habit: tabular crystals, subparallel aggregates, crusts.
Often confused with
Coquandite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads adamantine to pearly on Coquandite and resinous to subadamantine on Senarmontite.
How to tell apart: Stibiconite is the harder of the two (Mohs 5.5-7 vs. 3-4); streak differs, so Coquandite leaves white, Stibiconite leaves light yellow; luster reads adamantine to pearly on Coquandite and pearly, opaline, glassy to earthy on Stibiconite.
Often found alongside coquandite
Minerals reported to co-occur with coquandite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Sb₆.₃O₈.₃(SO₄)(OH)₀.₃(H₂O)₀.₉₇
- Mohs hardness
- 3-4
- Density
- 5.78 g/cm³
- Streak
- White
- Luster
- Adamantine to pearly
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
- Crystal habit
- Tabular crystals, subparallel aggregates, crusts
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Probably produced by action of H2SO4 on stibnite, in a stibnite vein in silicified limestone (Pereta mine, Italy)
Where rockhounds find coquandite
Classic worldwide localities
- Lucky Knock mine, Tonasket, Okanogan Co., Washington, USA
- Cetine mine, 20 km southwest of Siena, and the Pereta mine, Scansano, Tuscany, Italy
Field-hunting tip
Where it forms: Probably produced by action of H2SO4 on stibnite, in a stibnite vein in silicified limestone (Pereta mine, Italy). If you start seeing klebelsbergite, peretaite, valentinite in float, you are in the right ground. Typical habit: tabular crystals, subparallel aggregates, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
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Find coquandite on the map
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