Fourmarierite is a striking secondary uranium mineral characterized by its vibrant orange-red tabular crystals. It is typically found as an alteration product of uraninite in the oxidized zones of uranium deposits, often occurring in dense, subparallel clusters or crusts.

Hardness

3-4

Mohs

Luster

Adamantine to subadamantine

Streak

Orange

Transparency

Transparent to translucent

mineralrare

Fourmarierite

Hardness: 3-4
Luster: Adamantine to subadamantine
Streak: Orange
Transparency: Transparent to translucent

Is this fourmarierite?

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 fourmarierite with a known reference. Fourmarierite 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: orange.
3
Read the luster
Hold the specimen under a strong light. Luster: adamantine to subadamantine.
4
Match the color range
Compare against the expected color range: red, brown, carmine red, pink orange, reddish brown.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: pseudo hexagonal, tabular.

Often confused with

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

mineral

Becquerelite

Mohs 2.5

How to tell apart: Streak differs, so Fourmarierite leaves orange, Becquerelite leaves yellow.

How to tell apart: Streak differs, so Fourmarierite leaves orange, Vandenbrandeite leaves green; luster reads adamantine to subadamantine on Fourmarierite and vitreous on Vandenbrandeite.

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Often found alongside fourmarierite

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

All properties

Chemical formula: Pb(UO₂)₄O₃(OH)₄·4H₂O
Mohs hardness: 3-4
Density: 6.05 g/cm³
Colors: Red Brown Carmine redPink orangeReddish brown
Streak: Orange
Luster: Adamantine to subadamantine
Transparency: Transparent to translucent
Crystal system: Orthorhombic
Crystal habit: Pseudo hexagonal, tabular
Cleavage: {001}, perfect; {100}, imperfect
Rarity: Rare
Uses: Collector
Host rock: A rare secondary mineral formed as an alteration product of uraninite in the oxide zone of uranium deposits; a common component of “gummite” replacing uraninite; may replace fossil wood

Where rockhounds find fourmarierite

Classic worldwide localities

Palermo mine, near North Groton, Grafton Co., New Hampshire, USA
Newry, Oxford Co., Maine, USA
Liepers quarry, Swarthmore, Delaware Co., Pennsylvania, USA
Spruce Pine, Mitchell Co., North Carolina, USA
Relatively Shinkolobwe, Katanga Province, Congo (Shaba Province, Zaire)
Morogoro, Uluguru Mountains, Tanzania

Field-hunting tip

Where it forms: A rare secondary mineral formed as an alteration product of uraninite in the oxide zone of uranium deposits; a common component of “gummite” replacing uraninite; may replace fossil wood. If you start seeing uraninite, ianthinite, schoepite in float, you are in the right ground. Typical habit: pseudo hexagonal, tabular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify fourmarierite?+

Mohs hardness is 3-4. Luster: adamantine to subadamantine. The streak is orange. Common colors include red, brown, carmine red, pink orange.

Where is fourmarierite found?+

Notable localities include Palermo mine, near North Groton, Grafton Co., New Hampshire, USA; Newry, Oxford Co., Maine, USA; Liepers quarry, Swarthmore, Delaware Co., Pennsylvania, USA; Spruce Pine, Mitchell Co., North Carolina, USA; Relatively Shinkolobwe, Katanga Province, Congo (Shaba Province, Zaire).

Is fourmarierite safe to handle?+

Fourmarierite contains lead and uranium or thorium and calls for real care. Radioactive material; handle with minimal contact, store in a sealed lead-lined container, and wash hands thoroughly after handling. Do not ingest or inhale dust.

What rocks look like fourmarierite?+

Fourmarierite is most often confused with Becquerelite, Curite, Vandenbrandeite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with fourmarierite?+

Fourmarierite commonly co-occurs with Uraninite, Ianthinite, Schoepite, Becquerelite, Billietite, Dewindtite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does fourmarierite form in?+

Where it forms: A rare secondary mineral formed as an alteration product of uraninite in the oxide zone of uranium deposits; a common component of “gummite” replacing uraninite; may replace fossil wood. Working float back to the host body is the standard way to chase a fresh occurrence.

What is fourmarierite used for?+

Fourmarierite is used in collector.

Find fourmarierite on the map

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