Mapimite
Chemical formula: Zn²⁺₂Fe³⁺₃(As⁵⁺O₄)₃(OH)₄(H₂O)₄·6H₂O
Mapimite is a rare zinc and iron arsenate, forming characteristic spherical aggregates of tiny, green crystals.
Properties
- Mohs hardness
- 3
- Color
- Blue, blue-green, green
- Luster
- Vitreous
- Streak
- Light green
- Density
- 2.95
- Cleavage
- {001} and {010}.
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Mapimite is most easily recognized by its characteristic form of occurrence - spherical or radial aggregates of an intense green color. It forms crusts on host rocks, often in association with other colorful arsenates. ## Distinguishing from Similar Minerals It can be confused with other secondary green arsenate minerals such as scorodite, conichalcite, or agardite. It differs from scorodite by its aggregate form (mapimite forms spherical aggregates, scorodite more often forms druses with distinct crystals). It differs from agardite by its lighter shade of green and lower crystal transparency. Final distinction often requires advanced chemical analysis (EDS). ## Crystal Forms Crystals are very small, acicular or bladed, elongated along one axis. They usually occur as radial or spherulitic (spherical) aggregates, forming crusts and coatings on rock surfaces.
Geological environment
## Genesis Mapimite is a secondary mineral, forming in the oxidation (weathering) zones of polymetallic deposits rich in arsenic. It forms as a result of the weathering of arsenopyrite and other sulfides containing zinc and iron, under conditions of low temperature and pressure. ## Mineral Associations It most often co-occurs with other rare secondary minerals from the oxidation zone, such as adamite, ojuelaite, paradamite, legrandite, scorodite, smithsonite, as well as goethite and limonite. ## Localities The most important and classic locality for mapimite is the Ojuela Mine in Mapimí, Durango State, Mexico, from which the world's best specimens originate. It is also known from several other localities worldwide, including Laurion, Greece (Kamariza and Plaka mines) and the Tsumeb mine in Namibia, however, specimens from these places are much rarer and less spectacular than the Mexican ones.
Rarity
Very rare
For collectors
## Quality Criteria The most highly valued mapimite specimens are characterized by an intense, vivid, green color and well-formed, spherical aggregates. Contrast with the rock matrix is important - specimens on light limonite or goethite are desirable. The size of the aggregates and the coverage of the host rock surface also significantly affect the value. Specimens without mechanical damage, with a clearly visible radial structure, are the most sought after. ## Popular Localities Specimens from the type locality - the Ojuela Mine in Mexico - are by far the most valued and sought after by collectors. This locality has provided the largest number of specimens of the best quality, which set the standard for this mineral.
Care and storage
## Cleaning Mapimite specimens are extremely delicate and fragile. Cleaning should be kept to an absolute minimum. Only careful dust removal with a soft brush or a stream of compressed air from a safe distance is permissible. Any contact with water and chemical agents should be avoided. ## What to Avoid Absolutely avoid contact with water, acids, detergents, and other chemicals that can damage or dissolve the mineral. Mapimite is sensitive to shocks and impacts - its acicular crystals are easily crushed. It should be protected from high temperatures and direct sunlight, which can cause dehydration and color change. ## Storage Specimens should be stored in stable conditions, in closed, padded boxes or display cases, to protect them from dust, moisture, and mechanical damage. It is best to store it away from other, harder minerals to avoid scratching.