Moorhouseite
Chemical formula: Co<sup>2+</sup>S<sup>6+</sup>O<sub>4</sub>·6H<sub>2</sub>O
A rare, water-soluble cobalt sulfate, forming pink, acicular crystals and efflorescences.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous
- Streak
- White
- Density
- 1.927
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification The key diagnostic feature of moorhouseite is its complete solubility in water. Its pink color, acicular crystal habit, and occurrence as efflorescences in the oxidation zones of sulfide deposits (especially cobalt-bearing ones) are strong indicators. It reacts to changes in humidity, which is also a characteristic feature. ## Distinguishing from Similar Minerals It can be confused with other pink, hydrated sulfates, mainly bieberite (CoSO₄·7H₂O) and aplowite (CoSO₄·4H₂O). Bieberite crystallizes in the monoclinic system and contains more water, and its crystals can be better formed. Aplowite is a dehydration product of moorhouseite. Erythrite (cobalt arsenate) has a similar color but is insoluble in water and forms more flattened, bladed crystals. ## Crystal Forms It forms very fine, acicular or fibrous crystals, usually grouped into radial or tangled aggregates. It often occurs as crusts, coatings, and efflorescences on other minerals.
Geological environment
## Genesis Moorhouseite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits containing cobalt minerals, such as cobaltite or skutterudite. It forms under relatively low humidity conditions, often as a dehydration product of bieberite. It is a mineral typical of dry climates or mining environments where conditions are artificially dried. ## Mineral Associations It co-occurs with other secondary sulfates and arsenates. It is most commonly associated with bieberite, aplowite, melanterite, epsomite, morenosite, and erythrite. ## Localities The most important occurrences of this very rare mineral include the Walton mine in Nova Scotia, Canada (type locality); oxidation zones in the Bou Azzer region, Morocco; the mine in Jáchymov, Czech Republic; and some deposits in Saxony, Germany.
Rarity
Very rare
For collectors
## Quality Criteria The quality of a moorhouseite specimen is primarily assessed based on the abundance and preservation of its delicate crystals. Specimens with distinct, undamaged acicular aggregates of intense pink color, contrasting with the host rock, are most valued. Due to the mineral's instability, it is crucial that the specimen is well-preserved and shows no signs of dehydration (disintegration) or dissolution. ## Popular Localities The most well-known and valued specimens come from historical localities, such as the Bou Azzer region in Morocco, which has yielded specimens with well-formed aggregates. Material from the type locality in Canada also holds significant historical value for specialized collectors.
Care and storage
## Cleaning This mineral **must not be wet cleaned**, as it is completely soluble in water. Any contact with water, even a damp cloth, will cause its destruction. Dust can only be removed very carefully using a soft brush or a stream of dry air. ## What to Avoid Contact with water and other liquids must be strictly avoided. The mineral is sensitive to changes in humidity – in dry air, it dehydrates and may disintegrate, and in overly humid conditions, it may "melt away". It should be protected from high temperatures and direct sunlight. ## Storage Moorhouseite specimens require storage under special conditions. It is best to place them in a sealed, transparent container (e.g., a "perky box") or in a display case with controlled humidity. Isolation from air humidity fluctuations is crucial for preserving the specimen in an intact state.