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. Gaildunningite leaves a orange streak.
- 3Read the lusterHold the specimen under a strong light. Gaildunningite typically shows a vitreous to adamantine luster.
- 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; luster reads vitreous to adamantine on Gaildunningite and vitreous on Emmonsite.
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
Look in oxidized hydrothermal telluride deposits country, the host setting where gaildunningite typically forms. If you start seeing tellurite, emmonsite, quetzalcoatlite in float, you are in the right ground. Field specimens usually show a platy crystals, crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find gaildunningite on the map
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