Hephaistosite is an extremely rare thallium-mercury chloride mineral found exclusively in the ancient metallurgical slags of Laurion, Greece. It typically occurs as minute, vibrant yellow-green tabular crystals or crusts coating other rare secondary minerals in the slag environment.

Hardness

1.5-2

Mohs

Luster

Adamantine

Streak

Yellow

Transparency

Translucent

mineralrare

Hephaistosite

Hardness: 1.5-2
Luster: Adamantine
Streak: Yellow
Transparency: Translucent

Is this hephaistosite?

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 hephaistosite with a known reference. Hephaistosite sits at Mohs 1.5-2 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Hephaistosite leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Hephaistosite typically shows a adamantine luster.
4
Match the color range
Compare against the expected color range: bright yellow, yellow-green.
5
Look at form & habit
Crystal system: tetragonal. Typical habit: tabular crystals, crusts, coatings.

Often confused with

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

mineral

Calomel

Mohs 1.5-2

How to tell apart: Streak differs — Hephaistosite leaves yellow, Calomel leaves white.

How to tell apart: Laurionite is the harder of the two (Mohs 3-3.5 vs. 1.5-2); streak differs — Hephaistosite leaves yellow, Laurionite leaves white.

Compare →

Often found alongside hephaistosite

Minerals reported to co-occur with hephaistosite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: Tl₂Cl₂Hg
Mohs hardness: 1.5-2
Density: 7.33 g/cm³
Colors: Bright Yellow Yellow-green
Streak: Yellow
Luster: Adamantine
Transparency: Translucent
Crystal system: Tetragonal
Crystal habit: Tabular Crystals, Crusts, Coatings
Cleavage: None Observed
Rarity: Rare
Uses: Collector
Host rock: Ancient Lead-silver Mine Slags
Typical price: $200-1000+ per specimen

Where rockhounds find hephaistosite

Classic worldwide localities

Laurion, Greece

Field-hunting tip

Look in ancient lead-silver mine slags country — that is the host setting where hephaistosite typically forms. If you start seeing laurionite, fiedlerite, phosgenite in float, you are in the right ground. Field specimens usually show a tabular crystals, crusts, coatings habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify hephaistosite?+

Mohs hardness is 1.5-2. It typically shows a adamantine luster. The streak is yellow. Common colors include bright yellow, yellow-green.

Where is hephaistosite found?+

Notable localities include Laurion, Greece.

How much is hephaistosite worth?+

Typical asking prices fall in the range of $200-1000+ per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is hephaistosite safe to handle?+

It contains toxic constituents. Contains thallium and mercury, both of which are highly toxic; handle with extreme caution, wear gloves, and wash hands thoroughly after contact. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like hephaistosite?+

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

What minerals are found with hephaistosite?+

Hephaistosite commonly co-occurs with laurionite, fiedlerite, phosgenite, anglesite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does hephaistosite form in?+

Hephaistosite typically forms in ancient lead-silver mine slags. Working float back to the host body is the standard way to chase a fresh occurrence.

What is hephaistosite used for?+

Hephaistosite is used in collector.

Find hephaistosite on the map

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