Coquimbite is a rare hydrated iron sulfate mineral typically found as a secondary mineral in the oxidized zones of pyrite-bearing deposits. It is best identified by its delicate pale violet to white prismatic crystals, though it is highly soluble and must be kept in a dry environment to prevent dehydration and breakdown.
Is this coquimbite?
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 coquimbite with a known reference. Coquimbite 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: vitreous.
- 4Match the color rangeCompare against the expected color range: greenish white, bluish white, light violet, yellowish white, brownish white.
- 5Look at form & habitCrystal system: trigonal. Typical habit: massive, platy, prismatic.
Often confused with
Coquimbite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Coquimbite is noticeably harder (Mohs 2.5 vs. 1.5).
How to tell apart: Streak differs, so Coquimbite leaves white, Copiapite leaves pale yellow; luster reads vitreous on Coquimbite and pearly on {010} on Copiapite.
How to tell apart: Streak differs, so Coquimbite leaves white, Jarosite leaves pale yellow; luster reads vitreous on Coquimbite and subadamantine to vitreous, resinous on fractures on Jarosite.
Often found alongside coquimbite
Minerals reported to co-occur with coquimbite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- AlFe₃(SO₄)₆(H₂O)₁₂·6H₂O
- Mohs hardness
- 2.5
- Density
- 2.11 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Massive, platy, prismatic
- Cleavage
- Imperfect on {1011}; difficult on {1010}
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Typically a secondary mineral in the oxidized portions of weathering iron sulfide deposits in arid regions; rarely associated with fumarolic activity
Where rockhounds find coquimbite
Classic worldwide localities
- Bisbee, Cochise Co., and from the United Verde mine, Jerome, Yavapai Co., Arizona, USA
- Borate, San Bernardino Co., California, USA
- Dexter No. 7 mine, Calf Mesa, San Rafael district, Emery Co., Utah, USA
- Tierra Amarilla, southeast of Copiapó, Atacama, Chile
- Quetena, west of Calama, from Chuquicamata, and at Alcaparrosa, near Cerritos Bayos, southwest of Calama, Antofagasta, Chile
- Zalamea la Real, Huelva Province, Spain
Field-hunting tip
Where it forms: Typically a secondary mineral in the oxidized portions of weathering iron sulfide deposits in arid regions; rarely associated with fumarolic activity. If you start seeing copiapite, paracoquimbite, voltaite in float, you are in the right ground. Typical habit: massive, platy, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify coquimbite?+
Where is coquimbite found?+
What rocks look like coquimbite?+
What minerals are found with coquimbite?+
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Find coquimbite on the map
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