Guildite is a rare copper-iron sulfate mineral typically found as a secondary phase in the oxidized zones of metal mines. It usually presents as small, yellow, translucent tabular crystals or as crusty, granular masses. It is primarily sought after by advanced mineral collectors specializing in rare sulfate species.
Is this guildite?
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 guildite with a known reference. Guildite 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: pale canary-yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: brown, honey yellow, dark brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, massive, granular.
Often confused with
Guildite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Guildite leaves pale canary-yellow, Chalcanthite leaves white.
How to tell apart: Luster reads vitreous on Guildite and pearly on {010} on Copiapite.
How to tell apart: Streak differs, so Guildite leaves pale canary-yellow, Rozenite leaves white.
Often found alongside guildite
Minerals reported to co-occur with guildite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CuFe(SO₄)₂(OH)·4H₂O
- Mohs hardness
- 2.5
- Density
- 2.695-2.72 g/cm³
- Streak
- Pale canary-yellow
- Luster
- Vitreous
- Transparency
- Translucent to transparent in thin fragments
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, massive, granular
- Cleavage
- Perfect on {001} and {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral formed in mine workings by burning pyritic ores
Where rockhounds find guildite
Classic worldwide localities
- United Verde mine, Jerome, Yavapai Co., Arizona, USA
Field-hunting tip
Where it forms: A rare secondary mineral formed in mine workings by burning pyritic ores. If you start seeing coquimbite, ransomite in float, you are in the right ground. Typical habit: tabular crystals, massive, granular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify guildite?+
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Find guildite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
