Petersite-(La) is a rare secondary mineral typically found as fine, acicular, or fibrous radial sprays in oxidized copper deposits. It is most recognized for its vibrant blue to blue-green color and its association with other copper-bearing minerals like malachite.

Hardness

Mohs

Luster

Vitreous

Transparency

Translucent

mineralrareMixite Group family

Petersite-(La)

Hardness: ~3
Luster: Vitreous
Transparency: Translucent

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Is this petersite-(la)?

4-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 petersite-(la) with a known reference. Petersite-(La) sits at Mohs ~3, softer than the next harder reference, harder than the previous one.
2
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
3
Match the color range
Compare against the expected color range: yellowish green.
4
Look at form & habit
Crystal system: hexagonal. Typical habit: acicular or fibrous radial clusters.

Often confused with

Petersite-(La) vs. its common look-alikes, and how to tell them apart in the field.

Often found alongside petersite-(la)

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

All properties

Chemical formula: Cu₆La(PO₄)₃(OH)₆·3H₂O
Mohs hardness: ~3
Density: 3.33 g/cm³
Colors: Yellowish green
Luster: Vitreous
Transparency: Translucent
Crystal system: Hexagonal
Crystal habit: Acicular or fibrous radial clusters
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A secondary phase derived by weathering copper sulfides

Where rockhounds find petersite-(la)

Classic worldwide localities

Ohgurusu, Kiwa-cho, Kumano City, Mie Prefecture, Japan

Field-hunting tip

Where it forms: A secondary phase derived by weathering copper sulfides. If you start seeing pseudomalachite, malachite in float, you are in the right ground. Typical habit: acicular or fibrous radial clusters. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify petersite-(la)?+

Mohs hardness is ~3. Luster: vitreous. Common colors include yellowish green.

Where is petersite-(la) found?+

Notable localities include Ohgurusu, Kiwa-cho, Kumano City, Mie Prefecture, Japan.

Is petersite-(la) safe to handle?+

Petersite-(La) contains copper. Contains copper and potentially other heavy metals; avoid ingestion, inhalation of dust, and wash hands thoroughly after handling specimens.

What rocks look like petersite-(la)?+

Petersite-(La) is most often confused with Mixite, Clinoclase. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with petersite-(la)?+

Petersite-(La) commonly co-occurs with Pseudomalachite, Malachite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does petersite-(la) form in?+

Where it forms: A secondary phase derived by weathering copper sulfides. Working float back to the host body is the standard way to chase a fresh occurrence.

What is petersite-(la) used for?+

Petersite-(La) is used in collector.

Find petersite-(la) on the map

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