Omongwaite

Chemical formula: Na<sub>2</sub>Ca<sub>5</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>6</sub>·3H<sub>2</sub>O

Omongwaite is a rare hydrated sodium calcium sulfate, forming colorless, tabular crystals, discovered in the Omongwa mine in Namibia.

## Characteristics Omongwaite is a sulfate mineral that visually presents as colorless, transparent, tabular crystals. These crystals are typically small, reaching up to 0.2 mm in length and 0.02 mm in thickness. They occur as scattered, individual crystals or small aggregates on the surface of other minerals. ## Physical Properties The mineral is characterized by a vitreous luster. Its Mohs hardness is approximately 3. It is a relatively light mineral, with a density of 2.72 g/cm³. ## Colors and Varieties Omongwaite is colorless. No colored or commercial varieties have been distinguished. ## History and Name The mineral's name comes from its discovery locality – the Omongwa gypsum mine, located near the farm of the same name in the Omaheke region of Namibia. It was officially recognized by the International Mineralogical Association (IMA) in 2019 under number IMA2019-038. It was described by Gunnar Raade and his research team.

Properties

Mohs hardness
3
Luster
Vitreous
Streak
White
Density
2.72
Cleavage
Perfect on {100}
Fracture
Uneven
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Field identification of omongwaite is practically impossible due to its rarity and microscopic crystal size. In a collection, it can be recognized by its characteristic tabular appearance and its association with other minerals from the Omongwa mine. Final confirmation requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction. ## Distinguishing from Similar Minerals It can be confused with other colorless sulfates, such as gypsum or bassanite, which often occur in the same environment. Differentiation requires chemical and crystallographic analysis. It differs from gypsum in crystal habit and chemical composition (presence of sodium). ## Crystal Forms It forms thin, tabular crystals with a hexagonal outline, elongated in one direction. They occur as single, isolated crystals or small, loose aggregates.

Geological environment

## Genesis Omongwaite forms in an evaporitic environment, in sulfate-rich sediments. Its genesis at the type locality (Omongwa mine) is associated with the weathering of sulfide minerals in the presence of limestone and other sedimentary rocks in an arid climate. ## Mineral Associations This mineral co-occurs with other sulfates, such as gypsum, bassanite, syngenite, celestine, and with calcite. ## Localities The only confirmed occurrence of omongwaite worldwide is its type locality – the Omongwa gypsum mine in the Omaheke region of Namibia.

Rarity

Very rare

For collectors

## Quality Criteria As a "micromount" type mineral, its value is primarily determined by the quality and size of the crystals, even though they are microscopic. The most desirable specimens are those with well-formed, sharp, and transparent crystals that stand out clearly from the matrix. The richness of its association with other rare minerals is also important. ## Popular Localities The only source of specimens is the Omongwa mine in Namibia, which makes every specimen from this locality unique.

Care and storage

## Cleaning Due to the small size and fragility of the crystals, mechanical cleaning is not recommended. If dust removal is necessary, compressed air can be used from a safe distance. Contact with water is risky due to the solubility of sulfates. ## What to Avoid Avoid contact with water and any chemicals that could dissolve or damage the mineral. Due to its low hardness, it is susceptible to scratches. It should be protected from ultrasound and high temperatures. ## Storage Specimens of omongwaite should be stored under stable, dry conditions, preferably in sealed "micromount" boxes, which protect them from dust and mechanical damage.

Sources

Read more