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

2.5

Mohs

Luster

Adamantine

Streak

White

Transparency

Transparent

mineralrare

Penfieldite

Hardness: 2.5
Luster: Adamantine
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 2.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Penfieldite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Penfieldite typically shows a adamantine luster.
4
Match the color range
Compare against the expected color range: white, colorless.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: prismatic crystals, acicular.

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: 2.5
Density: 4.92 g/cm³
Colors: White Colorless
Streak: White
Luster: Adamantine
Transparency: Transparent
Crystal system: Hexagonal
Crystal habit: Prismatic Crystals, Acicular
Cleavage: Perfect Basal
Rarity: Rare
Uses: Collector
Host rock: Ancient Lead-smelting Slag Heaps
Typical price: $50-500 depending on specimen quality and rarity

Where rockhounds find penfieldite

Classic worldwide localities

Laurium, Greece
Sierra Gorda, Chile
Mammoth-Saint Anthony Mine, Arizona, USA

Field-hunting tip

Look in ancient lead-smelting slag heaps country — that is the host setting where penfieldite typically forms. If you start seeing laurionite, fiedlerite, cerussite in float, you are in the right ground. Field specimens usually show a prismatic crystals, acicular habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify penfieldite?+

Mohs hardness is 2.5. It typically shows a adamantine luster. The streak is white. Common colors include white, colorless.

Where is penfieldite found?+

Notable localities include Laurium, Greece; Sierra Gorda, Chile; Mammoth-Saint Anthony Mine, Arizona, USA.

How much is penfieldite worth?+

Typical asking prices fall in the range of $50-500 depending on specimen quality and rarity. Quality, size, and provenance can move individual specimens well outside that range.

Is penfieldite safe to handle?+

It contains toxic constituents. Contains lead; handle with care and wash hands thoroughly after contact. Do not inhale dust or ingestion. Handle with care, avoid grinding or breathing dust, and store separately.

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 Laurionite, Fiedlerite, Cerussite, Anglesite, Phosgenite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does penfieldite form in?+

Penfieldite typically forms in ancient lead-smelting slag heaps. 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.