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

3-4

Mohs

Luster

Vitreous

Streak

Pale Blue

Transparency

Translucent

mineralrareMixite Group family

Petersite-(La)

Hardness: 3-4
Luster: Vitreous
Streak: Pale Blue
Transparency: Translucent

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Is this petersite-(la)?

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 petersite-(la) with a known reference. Petersite-(La) 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. Petersite-(La) leaves a pale blue streak.
3
Read the luster
Hold the specimen under a strong light. Petersite-(La) typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: blue, blue-green, green.
5
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.

mineral

Mixite

Mohs 3-4

How to tell apart: Streak differs — Petersite-(La) leaves pale blue, Mixite leaves white.

How to tell apart: Streak differs — Petersite-(La) leaves pale blue, Clinoclase leaves bluish-green.

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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: (La,Ce,Nd,Ca)Cu₆(PO₄)₃(OH)₆·3H₂O
Mohs hardness: 3-4
Density: 4.2-4.5 g/cm³
Colors: Blue Blue-green Green
Streak: Pale Blue
Luster: Vitreous
Transparency: Translucent
Crystal system: Hexagonal
Crystal habit: Acicular or Fibrous Radial Clusters
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Oxidized Copper-bearing Hydrothermal Deposits
Typical price: $50-300 per specimen depending on size and quality

Where rockhounds find petersite-(la)

Classic worldwide localities

China
Czech Republic
France

Field-hunting tip

Look in oxidized copper-bearing hydrothermal deposits country — that is the host setting where petersite-(la) typically forms. If you start seeing malachite, azurite, limonite in float, you are in the right ground. Field specimens usually show a acicular or fibrous radial clusters habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify petersite-(la)?+

Mohs hardness is 3-4. It typically shows a vitreous luster. The streak is pale blue. Common colors include blue, blue-green, green.

Where is petersite-(la) found?+

Notable localities include China; Czech Republic; France.

How much is petersite-(la) worth?+

Typical asking prices fall in the range of $50-300 per specimen depending on size and quality. Quality, size, and provenance can move individual specimens well outside that range.

Is petersite-(la) safe to handle?+

It contains toxic constituents. Contains copper and potentially other heavy metals; avoid ingestion, inhalation of dust, and wash hands thoroughly after handling specimens. Handle with care, avoid grinding or breathing dust, and store separately.

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 Malachite, Azurite, Limonite. Spotting any of these in float or country rock is a useful trip signal.

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

Petersite-(La) typically forms in oxidized copper-bearing hydrothermal deposits. 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.