Gowerite

Chemical formula: Ca[B₅O₈(OH)][B(OH)₃]·₃H₂O

Gowerite is a rare, colorless or white hydrated calcium borate, forming aggregates of small, tabular crystals.

## Characteristics Gowerite is a hydrated calcium borate, rarely occurring in nature. It typically forms chalk-white, earthy, or chalk-like aggregates, which can also be seen as masses composed of very fine, colorless or white crystals. Individual crystals are in the form of thin tablets or laths, often grouped into rosette-like or radial aggregates. Due to the small size of the crystals, they are rarely visible to the naked eye. ## Physical properties Gowerite crystals exhibit a vitreous to pearly luster on cleavage surfaces. The mineral is soft, with a Mohs hardness of 3. It is relatively light, with a density close to 2 g/cm³. It is transparent to translucent. Gowerite is one of the borates that dissolve slowly in water. ## Colors and varieties This mineral is usually colorless, white, or grayish. No colored varieties or trade names are distinguished for it. ## History and name The name gowerite honors John Gower (1881-1962), a long-time employee of the Pacific Coast Borax Company in California, USA. The mineral was first described in 1959 by Carl L. Christ and Joan R. Clark based on material found in Death Valley. ## Uses Due to its rarity and small size, gowerite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or borate minerals.

Properties

Mohs hardness: 3
Luster: Vitreous
Streak: White
Density: 1.99
Cleavage: Perfect on {100}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Its chalk-white, earthy, or microcrystalline aggregates occurring in borate evaporite environments are characteristic. Gowerite is very soft (hardness 3) and soluble in water. The reaction to hydrochloric acid is slow and without effervescence. Identification usually requires advanced methods, such as X-ray diffraction (XRD). ## Distinguishing from similar minerals It can be confused with other white, earthy borates, such as colemanite, ulexite, or hydroboracite, with which it often co-occurs. Ulexite often forms characteristic fibrous aggregates ("TV rock"), and colemanite has a higher hardness (4.5). Certain distinction without laboratory analysis is very difficult. ## Crystal forms Gowerite crystallizes as very small, thin, tabular or lath-like crystals, often grouped into rosette-like or radial aggregates. It also forms massive, earthy, and chalk-like aggregates.

Geological environment

## Genesis Gowerite is a secondary mineral, formed as a result of weathering or alteration processes of primary borate deposits in desert (evaporitic) environments. It forms under low temperature and pressure conditions in playa-type sediments (dried salt lakes). ## Mineral associations It most commonly co-occurs with other borate minerals, such as colemanite, ulexite, hydroboracite, gypsum, as well as with calcite and aluminosilicates. ## Localities The most important and classic localities for gowerite are in the USA, in California, in the Death Valley region (Inyo County), especially in borate mines such as Corkscrew Canyon and Gower Gulch. It has also been reported in Argentina (Salta Province) and Turkey.

Rarity

Rare

For collectors

## Quality criteria For collectors, the most valuable specimens are those with visible, even if small, well-formed crystals in the form of rosettes or radial aggregates on matrix. Purity and lack of damage are crucial, which is difficult to achieve due to the mineral's brittleness. Contrast with darker host rock enhances the specimen's attractiveness. ## Popular localities The most prized specimens come from historical localities in Death Valley, California, USA. These are considered classic and most desired by borate mineral specialists.

Care and storage

## Cleaning Clean only dry, using a soft brush to remove dust. Gowerite is soluble in water, so contact with it is absolutely forbidden. ## What to avoid Contact with water and other liquids must be strictly avoided, as the mineral will dissolve. It should be protected from high humidity, which can also lead to its degradation. Avoid ultrasound and all chemical agents. It is a very soft and brittle mineral, sensitive to mechanical damage. ## Storage Gowerite specimens must be stored in a dry place, preferably in an airtight container (e.g., a "membrane box") with a desiccant (e.g., silica gel). Keep it away from heat sources and protect it from dust.

Sources

IMA Mineral List (CNMNC)