Woodwardite
Chemical formula: (Cu²⁺,Al)₉(S⁶⁺O₄)₂(OH)₁₈·nH₂O
Woodwardite is a rare secondary mineral characterized by its blue to greenish-blue color, forming rosette aggregates and crusts.
Properties
- Mohs hardness
- 2
- Color
- Greenish-blue, turquoise-blue
- Luster
- Pearly
- Streak
- Pale blue
- Density
- 2.38
- Cleavage
- Perfect on {0001}
- Fracture
- Uneven
- Transparency
- Translucent,Opaque
- Crystal system
- Trigonal
Diagnostic features
## Identification Woodwardite can be identified by its characteristic blue color, low hardness, and typical forms of occurrence – spherical aggregates and crusts. It often forms thin coatings on other minerals or host rock. ## Distinguishing from Similar Minerals It can be confused with other secondary copper minerals such as aurichalcite, cyanotrichite, or rosasite. Aurichalcite has a similar habit but usually a lighter, more sky-blue hue. Cyanotrichite forms acicular or fibrous crystals in radial aggregates. Rosasite is harder (approx. 4 on the Mohs scale) and often forms crusts with a zoned structure. Definitive distinction often requires chemical analysis. ## Crystal Forms Woodwardite crystallizes as very small, hexagonal plates. It mainly forms spherical, spherulitic, and rosette aggregates, as well as thin crusts and coatings with a fibrous or radial structure.
Geological environment
## Genesis It is a secondary mineral, forming in the oxidation (weathering) zones of copper ore deposits. It forms as a result of sulfate-rich waters acting on rocks containing copper and aluminum, often in voids and fissures in rocks. It is a product of post-magmatic processes. ## Mineral Associations It often co-occurs with other secondary copper and zinc minerals, such as malachite, azurite, brochantite, linarite, aurichalcite, hemimorphite, as well as goethite and quartz. ## Localities Key localities worldwide include Cornwall (Great Britain - type locality), mines in the Laurion region (Greece), the Atacama Desert (Chile), and the states of Arizona and Utah (USA). It also occurs in small quantities in many other places around the world where copper deposits are oxidizing.
Rarity
Rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-formed, spherical or rosette aggregates of intense, uniform blue color. Contrast with the rock matrix and the absence of damage to delicate structures are also important. Large, rich crusts are also sought after. ## Popular Localities Classic and best-known specimens come from historical mines in Cornwall (Great Britain). High-quality woodwardite, often in association with other rare minerals, also comes from the mines in Laurion, Greece.
Care and storage
## Cleaning Woodwardite specimens are extremely delicate and sensitive to water. They should not be washed with water or any liquids. To remove dust, a very soft brush or compressed air from a distance can be used very carefully. ## What to Avoid Contact with water, acids, detergents, and other chemicals must be strictly avoided. The mineral is very soft and susceptible to scratches and mechanical damage. It should be protected from high temperatures, which can cause dehydration and structural damage. ## Storage It is recommended to store specimens in closed, dry containers or display cases, away from sources of moisture and dust. It is best to keep it in its original collector's box (a "perky box") to minimize the risk of damage.