Penfieldite is a rare lead chloride mineral that typically forms as white, adamantine, hexagonal prismatic crystals. It is most famously associated with the ancient slag piles of Laurium, Greece, where it forms through the slow chemical alteration of lead-rich slag by seawater.

Hardness

3-4

Mohs

Luster

Adamantine to greasy

Streak

White

Transparency

Transparent

mineralrare

Penfieldite

Hardness: 3-4
Luster: Adamantine to greasy
Streak: White
Transparency: Transparent

Is this penfieldite?

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 penfieldite with a known reference. Penfieldite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: adamantine to greasy.
4
Match the color range
Compare against the expected color range: white, colorless, yellowish, bluish.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: pyramidal, tabular.

Often confused with

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

Often found alongside penfieldite

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

All properties

Chemical formula: Pb₂Cl₃(OH)
Mohs hardness: 3-4
Density: 5.82-6.61 g/cm³
Colors: White Colorless Yellowish Bluish
Streak: White
Luster: Adamantine to greasy
Transparency: Transparent
Crystal system: Hexagonal
Crystal habit: Pyramidal, tabular
Cleavage: {0001}, distinct
Rarity: Rare
Uses: Collector
Host rock: An alteration product of lead-bearing slag immersed in seawater (Laurium, Greece; Baratti Beach, Italy); in an oxidized hydrothermal lead deposit (Sierra Gorda district, Chile)

Where rockhounds find penfieldite

Classic worldwide localities

Laurium, Greece, in slag
Baratti Beach, Tuscany, Italy, in slag
Margarita mine, Sierra Gorda district, southwest of Calama, Antofagasta, Chile

Field-hunting tip

Where it forms: An alteration product of lead-bearing slag immersed in seawater (Laurium, Greece; Baratti Beach, Italy); in an oxidized hydrothermal lead deposit (Sierra Gorda district, Chile). If you start seeing paralaurionite, phosgenite, fiedlerite in float, you are in the right ground. Typical habit: pyramidal, tabular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify penfieldite?+

Mohs hardness is 3-4. Luster: adamantine to greasy. The streak is white. Common colors include white, colorless, yellowish, bluish.

Where is penfieldite found?+

Notable localities include Laurium, Greece, in slag; Baratti Beach, Tuscany, Italy, in slag; Margarita mine, Sierra Gorda district, southwest of Calama, Antofagasta, Chile.

Is penfieldite safe to handle?+

Penfieldite contains lead. Contains lead; handle with care and wash hands thoroughly after contact. Do not inhale dust or ingestion.

What rocks look like penfieldite?+

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

What minerals are found with penfieldite?+

Penfieldite commonly co-occurs with Paralaurionite, Phosgenite, Fiedlerite, Cotunnite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does penfieldite form in?+

Where it forms: An alteration product of lead-bearing slag immersed in seawater (Laurium, Greece; Baratti Beach, Italy); in an oxidized hydrothermal lead deposit (Sierra Gorda district, Chile). Working float back to the host body is the standard way to chase a fresh occurrence.

What is penfieldite used for?+

Penfieldite is used in collector.

Find penfieldite on the map

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