Erythrite Mineral Overview
Mineral name: Erythrite
Mineral class: Arsenate
Known Facts
- Chemical formula: Co₃(AsO₄)₂·8H₂O
- Crystal system: Monoclinic
- Mohs hardness: 1.5–2.5
- Color range: Bright pink, crimson, purple-pink
- Luster: Vitreous to pearly
- Streak: Pale pink
- Cleavage: Perfect in one direction
- Fracture: Uneven to splintery
- Specific gravity: Approximately 3.0–3.1
- Common locations: Morocco, Germany, Canada, United States, Australia
- Uses: Indicator mineral for cobalt, collector specimens
- Similar minerals: Annabergite, roselite, cobaltite (primary ore)
Physical and Optical Characteristics
Erythrite is easily recognized by its vivid pink to crimson color, which makes it one of the most distinctive secondary minerals.
It typically forms:
- Acicular (needle-like) crystals
- Radiating sprays or starburst clusters
- Fibrous crusts and coatings
Crystals are often transparent to translucent, though aggregates may appear more opaque.
The luster is vitreous on crystal faces and pearly on cleavage surfaces. Due to its low hardness (1.5–2.5), erythrite is very soft and fragile.
Chemical Composition and Structure
Erythrite is a hydrated cobalt arsenate, with the formula:
- Co₃(AsO₄)₂·8H₂O
Key components include:
- Cobalt (Co²⁺) — responsible for its intense pink color
- Arsenate groups (AsO₄³⁻)
- Water molecules (H₂O) within the structure
It belongs to the vivianite group, which includes similar hydrated arsenates and phosphates.
Erythrite forms a series with:
- Annabergite (Ni₃(AsO₄)₂·8H₂O) — nickel-rich, typically green
Formation and Geological Occurrence
Erythrite forms as a secondary mineral in the oxidation zones of cobalt-bearing deposits.
Typical formation processes include:
- Weathering of primary cobalt minerals such as cobaltite
- Reaction with arsenic-bearing fluids
- Deposition in oxidizing environments
It is commonly found as:
- Coatings on rock surfaces
- Crystals in fractures and cavities
Associated minerals include:
- Cobaltite
- Annabergite
- Skutterudite
- Iron oxides and other secondary minerals
Common Locations
Notable occurrences of Erythrite include:
- Morocco: Bou Azzer district (well-known for bright specimens)
- Germany: Classic European localities
- Canada: Ontario cobalt mining regions
- United States: Nevada, Idaho
- Australia: Cobalt-rich deposits
Moroccan specimens are particularly известны for their color and crystal quality.
Uses and Practical Significance
Erythrite has no industrial use but is important for:
- Indicator mineral: Signals the presence of cobalt ore
- Mineral collecting: Highly valued for its vivid color and crystal sprays
Because it contains arsenic, it should be handled with care.
Similar and Related Minerals
Erythrite may be confused with other colorful secondary minerals:
- Annabergite: Green nickel arsenate
- Roselite: Pink cobalt arsenate but typically forms different crystal habits
- Cobaltite: Primary cobalt mineral, metallic and not pink
Distinguishing features include:
- Bright pink color
- Acicular crystal sprays
- Occurrence in oxidized cobalt deposits
Identification Notes for Collectors
- Look for bright pink, needle-like crystal sprays
- Note association with cobalt minerals
- Check for softness and perfect cleavage
- Observe occurrence as coatings in oxidation zones
- Handle carefully due to arsenic content
Erythrite is a striking cobalt arsenate mineral, recognized for its intense pink color and radiating crystal habit, and is an important visual indicator of cobalt mineralization.