Tocornalite is a rare silver-mercury iodide mineral found in the oxidation zones of silver-rich mineral deposits. It typically occurs as massive, dull-yellow, earthy crusts or coatings on other silver halides and is highly sought after by advanced collectors of rare silver minerals.
Is this tocornalite?
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 tocornalite with a known reference. Tocornalite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: earthy.
- 4Match the color rangeCompare against the expected color range: yellow, bright yellow, gray green, black.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: massive.
Often confused with
Tocornalite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads earthy on Tocornalite and resinous to adamantine, pearly on cleavage surfaces on Iodargyrite.
How to tell apart: Streak differs, so Tocornalite leaves yellow, Miargyrite leaves cherry-red; luster reads earthy on Tocornalite and metallic adamantine on Miargyrite.
Often found alongside tocornalite
Minerals reported to co-occur with tocornalite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ag,Hg)I
- Mohs hardness
- 2-3
- Density
- 5.7-5.9 g/cm³
- Streak
- Yellow
- Luster
- Earthy
- Transparency
- Semitransparent
- Crystal system
- Hexagonal
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a very rich hydrothermal silver deposit
Where rockhounds find tocornalite
Classic worldwide localities
- Chañarcillo, south of Copiapó, Atacama, Chile
Field-hunting tip
Where it forms: In a very rich hydrothermal silver deposit. If you start seeing iodargyrite, cerargyrite, native silver in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tocornalite?+
Where is tocornalite found?+
Is tocornalite safe to handle?+
What rocks look like tocornalite?+
What minerals are found with tocornalite?+
What kind of rock does tocornalite form in?+
What is tocornalite used for?+
Find tocornalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
