RockHoundR

Erythrite is a secondary mineral often called 'cobalt bloom' because it forms as bright pink to crimson crusts on weathered cobalt-arsenide deposits. It is best known for its delicate, acicular prismatic crystals or radiating sprays, though these are extremely fragile and must be handled with great care.

Hardness
1.5-2.5
Mohs
Luster
Subadamantine, pearly on cleavages
Streak
Pale red to pink
Transparency
Transparent to translucent

Is this erythrite?

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 erythrite with a known reference. Erythrite sits at Mohs 1.5-2.5, softer than the next harder reference, harder than the previous one.
  • 2
    Check the streak
    Drag the specimen across an unglazed porcelain plate. Streak: pale red to pink.
  • 3
    Read the luster
    Hold the specimen under a strong light. Luster: subadamantine, pearly on cleavages.
  • 4
    Match the color range
    Compare against the expected color range: crimson, peach-red, pink, violet, colorless, violet red, light pink, purple red.
  • 5
    Look at form & habit
    Crystal system: monoclinic. Typical habit: divergent, prismatic, striated.

Often confused with

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

Vivianite mineral
mineral
Vivianite
Mohs 1.5-2

How to tell apart: Streak differs, so Erythrite leaves pale red to pink, Vivianite leaves white, altering to dark blue, brown; luster reads subadamantine, pearly on cleavages on Erythrite and vitreous, pearly on the cleavage, dull when earthy on Vivianite.

Compare →

Often found alongside erythrite

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

All properties

Chemical formula
Co₃(AsO₄)₂·8H₂O
Mohs hardness
1.5-2.5
Density
3.06 g/cm³
Colors
CrimsonPeach-redPinkVioletColorlessViolet redLight pinkPurple red
Streak
Pale red to pink
Luster
Subadamantine, pearly on cleavages
Transparency
Transparent to translucent
Crystal system
Monoclinic
Crystal habit
Divergent, prismatic, striated
Cleavage
Perfect on {010}; poor on {100} and {102}
Rarity
Uncommon
Uses
Collector, Indicator mineral
Host rock
A secondary mineral in the oxide zone of some Co–Ni–As-bearing mineral deposits

Where rockhounds find erythrite

1 mapped spots

Classic worldwide localities

  • Blackbird mine, Lemhi Co., Idaho, USA
  • Chalanches, near Allemont, Isère, France
  • Fine examples Schneeberg, Saxony, at Wittichen, Black Forest, from Richelsdorf, Hesse, Germany
  • Jáchymov (Joachimsthal), Czech Republic
  • Botallack mine, St. Just, and from a number of other places in Cornwall, England
  • Aghbar (Arhbar), Irhtem (Ightem), and other mines in the Bou Azzer district, Morocco

Field-hunting tip

Where it forms: A secondary mineral in the oxide zone of some Co–Ni–As-bearing mineral deposits. If you start seeing cobaltite, skutterudite, symplesite in float, you are in the right ground. Typical habit: divergent, prismatic, striated. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Wyoming. Start trip planning there.

Browse 1 U.S. spots for erythrite →

Common questions

How do you identify erythrite?+
Mohs hardness is 1.5-2.5. Luster: subadamantine, pearly on cleavages. The streak is pale red to pink. Common colors include crimson, peach-red, pink, violet.
Where is erythrite found?+
Notable localities include Blackbird mine, Lemhi Co., Idaho, USA; Chalanches, near Allemont, Isère, France; Fine examples Schneeberg, Saxony, at Wittichen, Black Forest, from Richelsdorf, Hesse, Germany; Jáchymov (Joachimsthal), Czech Republic; Botallack mine, St. Just, and from a number of other places in Cornwall, England.
Can I find erythrite in the United States?+
RockHoundR maps 1 erythrite rockhounding spots across 1 U.S. states. The top states are Wyoming.
Is erythrite safe to handle?+
Erythrite contains arsenic and cobalt and calls for real care. Contains arsenic and cobalt; wash hands thoroughly after handling and avoid inhaling dust or powder.
What rocks look like erythrite?+
Erythrite is most often confused with Vivianite. A quick hardness test and a streak check separate the look-alikes faster than color alone.
What minerals are found with erythrite?+
Erythrite commonly co-occurs with Cobaltite, Skutterudite, Symplesite, Roselite-beta, Scorodite, Pharmacosiderite. Spotting any of these in float or country rock is a useful trip signal.
What kind of rock does erythrite form in?+
Where it forms: A secondary mineral in the oxide zone of some Co–Ni–As-bearing mineral deposits. Working float back to the host body is the standard way to chase a fresh occurrence.
What is erythrite used for?+
Erythrite is used in collector, indicator mineral.

Find erythrite on the map

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