Gajardoite is a rare potassium calcium arsenic oxide that forms colorless hexagonal plates. Associated minerals include arsenolite, chongite and talmessite. It was first described from Torrecillas mine, northern Atacama Desert, Iquique Province, Tarapacá Region, Chile.
Is this gajardoite?
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 gajardoite with a known reference. Gajardoite sits at Mohs ~1.5, 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: colorless.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: tabular, pseudo-hexagonal crystals.
Often confused with
Gajardoite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Pharmacosiderite is the harder of the two (Mohs 2.5 vs. ~1.5); streak differs, so Gajardoite leaves white, Pharmacosiderite leaves yellowish green; luster reads vitreous on Gajardoite and adamantine to greasy on Pharmacosiderite.
How to tell apart: Scorodite is the harder of the two (Mohs 3.5-4 vs. ~1.5); streak differs, so Gajardoite leaves white, Scorodite leaves greenish white.
Often found alongside gajardoite
Minerals reported to co-occur with gajardoite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KCa₀.₅As³⁺₄O₆Cl₂·5H₂O
- Mohs hardness
- ~1.5
- Density
- 2.64 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Hexagonal
- Crystal habit
- Tabular, pseudo-hexagonal crystals
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral from the oxidation of native arsenic and other As-bearing primary phases,followed by later alteration by saline fluids derived from evaporating meteoric water under hyperarid conditions
Where rockhounds find gajardoite
Classic worldwide localities
- Torrecillas mine, northern Atacama Desert, Iquique Province, Tarapacá Region, Chile
- Village of Cuya in the Camarones Valley, Arica Province, Chile
Field-hunting tip
Where it forms: A secondary mineral from the oxidation of native arsenic and other As-bearing primary phases,followed by later alteration by saline fluids derived from evaporating meteoric water under hyperarid conditions. If you start seeing native arsenic, arsenolite, chongite in float, you are in the right ground. Typical habit: tabular, pseudo-hexagonal crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gajardoite?+
Where is gajardoite found?+
Is gajardoite safe to handle?+
What rocks look like gajardoite?+
What minerals are found with gajardoite?+
What kind of rock does gajardoite form in?+
What is gajardoite used for?+
Find gajardoite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
