Gaildunningite is a rare mercury halide. It was approved as a distinct mineral species in 2018. It was first described from Clear Creek mine, New Idria mining district, San Benito Co., California, USA.
Is this gaildunningite?
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 gaildunningite with a known reference. Gaildunningite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: orange.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to adamantine.
- 4Match the color rangeCompare against the expected color range: yellow, orange, darker orange-red.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy crystals, crusts.
Often confused with
Gaildunningite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Gaildunningite leaves orange, Tellurite leaves white; luster reads vitreous to adamantine on Gaildunningite and subadamantine on Tellurite.
How to tell apart: Emmonsite is the harder of the two (Mohs ~5 vs. 2); streak differs, so Gaildunningite leaves orange, Emmonsite leaves pale yellow.
Often found alongside gaildunningite
Minerals reported to co-occur with gaildunningite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Hg²⁺₃[NHg²⁺₂]₁₈(Cl,I)₂₄
- Mohs hardness
- 2
- Density
- 8.22 g/cm³
- Streak
- Orange
- Luster
- Vitreous to adamantine
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy crystals, crusts
- Cleavage
- Very good on {100} and {010}, good on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- oxidized hydrothermal telluride deposits
Where rockhounds find gaildunningite
Classic worldwide localities
- Centennial Eureka mine, Utah, USA
Field-hunting tip
Where it forms: oxidized hydrothermal telluride deposits. If you start seeing tellurite, emmonsite, quetzalcoatlite in float, you are in the right ground. Typical habit: platy crystals, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gaildunningite?+
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What rocks look like gaildunningite?+
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Find gaildunningite on the map
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