Joosteite

Chemical formula: Mn₂+Mn₃+O(PO₄)

Joosteite is a rare manganese phosphate, forming black, platy crystals with a metallic luster, found in granitic pegmatites.

## Characteristics Joosteite is a mineral from the phosphate group, chemically a hydrated manganese phosphate (with both II and III oxidation states). It occurs as small, platy or bladed crystals, usually not exceeding 1 mm in length. It forms radial aggregates or occurs as single crystals embedded in the rock. Its characteristic features are its black color and strong, metallic luster. ## Physical Properties This mineral is characterized by a hardness of approximately 5 on the Mohs scale. It has a strong, metallic to submetallic luster. It is opaque. The calculated density is approximately 3.93 g/cm³. It exhibits perfect cleavage in one direction. ## Colors and Varieties Joosteite is a mineral of uniform, black color. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name honors Ian Jooste, a South African mineral collector who first found this mineral. It was described and approved as a new mineral species by the International Mineralogical Association (IMA) in 2003 (IMA2003-047). The discovery was made at Sandamap Farm, Erongo Region, Namibia. ## Uses Due to its extreme rarity and small crystal size, joosteite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals (so-called "micromounts") and scientists.

Properties

Mohs hardness: 4
Color: grey with a brownish tinge, dark brown in thin section
Luster: Metallic to submetallic
Streak: Black
Density: 0
Cleavage: Perfect on {100}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Joosteite can be identified by its black color, strong metallic luster, and characteristic form of small, platy crystals. Its occurrence is limited to a specific geological environment - granitic pegmatites. ## Distinguishing from Similar Minerals It can be confused with other black, metallic-lustered phosphate minerals or oxides found in pegmatites, such as wolframite, pyrophanite, or ilmenite. Final differentiation from these minerals requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS/WDS), due to visual similarity and small crystal sizes. ## Crystal Forms It forms flattened, platy or bladed crystals, often grouped into radial aggregates. Crystals are usually very small, rarely exceeding 1 mm.

Geological environment

## Genesis Joosteite is a mineral of secondary origin. It forms in complex, phosphate-rich granitic pegmatites. It develops as a result of hydrothermal processes or weathering, replacing earlier phosphate minerals, especially lithiophilite. ## Mineral Associations This mineral co-occurs with other phosphates at its discovery site. It is most commonly associated with lithiophilite, strengite, hureaulite, tancoite, eosphorite, and quartz. ## Localities The only confirmed and described locality of joosteite in the world is its type locality - Sandamap Farm (Sandamap North pegmatite) in the Daures District, Erongo Region, Namibia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a joosteite specimen is primarily assessed based on the sharpness and development of the crystals, as well as their size, although they always remain small. Specimens with clearly formed, undamaged platy crystals that form aesthetic aggregates are most valued. The contrast with the surrounding rock (matrix) and the presence of well-identified associated minerals are also important. ## Popular Localities The only source of joosteite specimens is its type locality in Namibia. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Joosteite specimens should only be cleaned very carefully, using a soft brush to remove dust. Due to its rarity and potential reactivity, contact with water and any chemical agents should be avoided. Dry cleaning is the safest method. ## What to Avoid Ultrasonic cleaners, strong chemicals, acids, and bases must be absolutely avoided. The mineral may be sensitive to sudden temperature changes. It should not be exposed to prolonged moisture. ## Storage Joosteite specimens, typically micromounts, are best stored in dedicated, sealed perky boxes, which protect them from dust, moisture, and mechanical damage. Avoid storing in areas with high air humidity.

External references

https://www.mindat.org/min-27436.html