Despujolsite
Chemical formula: Ca₃Mn⁴⁺(S⁶⁺O₄)₂(OH)₆·3H₂O
Despujolsite is a rare sulfate mineral, distinguished by its characteristic, intensely yellow color and occurrence as small, hexagonal crystals.
Properties
- Mohs hardness
- 2.5
- Color
- Pale yellow to deep yellow-green
- Luster
- Vitreous
- Streak
- Pale yellow
- Density
- 2.46
- Cleavage
- Perfect on {1010}
- Fracture
- Conchoidal
- Transparency
- Transparent
- Crystal system
- Hexagonal
Diagnostic features
## Identification Despujolsite is relatively easy to identify based on its intense, lemon-yellow color, hexagonal crystal form, and characteristic radial aggregates. Its low hardness (about 2.5 on the Mohs scale) is also an important diagnostic feature. It reacts vigorously with hydrochloric acid, which is a confirmatory test. ## Distinguishing from Similar Minerals Due to its unique color and form, despujolsite is difficult to confuse with other minerals. Some yellow secondary minerals may appear similar from a distance but differ in crystal form and reaction to acids. ## Crystal Forms Despujolsite crystals are hexagonal, with a prismatic habit, often elongated along the crystallographic axis. Crystal terminations can be flat (pinacoidal). Most commonly, it forms radial aggregates of small, acicular crystals, as well as rosettes and spherulitic clusters.
Geological environment
## Genesis Despujolsite is a secondary mineral, forming in the oxidation zones of manganese deposits. It forms as a result of low-temperature hydrothermal processes acting on rocks rich in calcium and sulfides. Its formation is associated with the weathering of primary manganese ores in the presence of sulfate-rich solutions. ## Mineral Associations This mineral often co-occurs with other manganese minerals and sulfates. The most common associations include: calcite, gypsum, marokite, gaudefroyite, hausmannite, braunite, and other manganese oxides. ## Localities The most important and classic locality for despujolsite, from which the world's best specimens originate, is the Tachgagalt mine in Ouarzazate Province, Morocco. This is its type locality. It is also known from several other occurrences worldwide, including the N'Chwaning mine in the Kalahari Manganese Fields complex in South Africa.
Rarity
Rare
For collectors
## Quality Criteria Specimens with well-formed, sharp crystals of intense, lemon-yellow color are most prized by collectors. Rich, radial aggregates forming aesthetic compositions on a rock matrix, especially in contrast with dark manganese oxides or white calcite, are also highly valued. The size of the crystals, their transparency, and the absence of mechanical damage significantly increase the specimen's value. ## Popular Localities By far the most sought-after and highly valued despujolsite specimens come from its type locality – the Tachgagalt mine in Morocco. Specimens from South Africa, though also valuable, are generally rarer on the collector's market.
Care and storage
## Cleaning Despujolsite specimens are very delicate and sensitive. They should be cleaned only very carefully, using a soft brush to remove dust. Due to its solubility, contact with water, and especially acids, should be avoided. ## What to Avoid The mineral is sensitive to acids, in which it dissolves rapidly. Avoid cleaning in ultrasonic cleaners, chemical cleaning, and exposure to high temperatures, which can lead to dehydration and structural damage. It should be protected from moisture. ## Storage Despujolsite specimens are best stored in closed, dry containers or display cases to protect them from dust, moisture, and mechanical damage. Due to its softness, it should not be stored in contact with harder minerals.