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.

Hardness

2-3

Mohs

Luster

Resinous

Streak

Yellow

Transparency

Opaque

mineralrareIodargyrite Group family

Tocornalite

Hardness: 2-3
Luster: Resinous
Streak: Yellow
Transparency: Opaque

Is this tocornalite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch tocornalite with a known reference. Tocornalite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Tocornalite leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Tocornalite typically shows a resinous luster.
4
Match the color range
Compare against the expected color range: yellow, pale yellow, brownish yellow.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: massive, crusts, coatings.

Often confused with

Tocornalite vs. its common look-alikes, and how to tell them apart in the field.

How to tell apart: Streak differs, so Tocornalite leaves yellow, Miargyrite leaves cherry-red; luster reads resinous on Tocornalite and metallic to submetallic on Miargyrite.

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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
Colors: Yellow Pale Yellow Brownish Yellow
Streak: Yellow
Luster: Resinous
Transparency: Opaque
Crystal system: Hexagonal
Crystal habit: Massive, Crusts, Coatings
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Oxidized Zones of Silver Deposits
Typical price: $50-300 per specimen depending on size and provenance

Where rockhounds find tocornalite

Classic worldwide localities

Chañarcillo, Chile
Broken Hill, Australia

Field-hunting tip

Look in oxidized zones of silver deposits country, the host setting where tocornalite typically forms. If you start seeing iodargyrite, cerargyrite, native silver in float, you are in the right ground. Field specimens usually show a massive, crusts, coatings habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify tocornalite?+

Mohs hardness is 2-3. It typically shows a resinous luster. The streak is yellow. Common colors include yellow, pale yellow, brownish yellow.

Where is tocornalite found?+

Notable localities include Chañarcillo, Chile; Broken Hill, Australia.

How much is tocornalite worth?+

Typical asking prices fall in the range of $50-300 per specimen depending on size and provenance. Quality, size, and provenance can move individual specimens well outside that range.

Is tocornalite safe to handle?+

It contains toxic constituents. Contains mercury and silver; wash hands thoroughly after handling and avoid inhaling dust or ingesting particles. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like tocornalite?+

Tocornalite is most often confused with Iodargyrite, Miargyrite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with tocornalite?+

Tocornalite commonly co-occurs with Iodargyrite, Cerargyrite, Native Silver. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does tocornalite form in?+

Tocornalite typically forms in oxidized zones of silver deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is tocornalite used for?+

Tocornalite is used in collector.

Find tocornalite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.