Walkerite

Chemical formula: Ca₁₆(Mg,Li)₂[B₁₃O₁₇(OH)₁₂]₄Cl₆·₂₈H₂O

Walkerite is an extremely rare, hydrated calcium, magnesium, and lithium borate, forming colorless, tabular crystals.

## Characteristics Walkerite is an exceptionally rare mineral from the borate group, with a complex chemical composition containing calcium, magnesium, lithium, chlorine, and water. It occurs as small, colorless, tabular crystals, which can form rosette-like or spherical aggregates. Due to its rarity and small crystal size, it is a mineral known primarily within scientific and specialized circles. ## Physical Properties Walkerite crystals exhibit a vitreous luster. They are transparent and colorless. This mineral is relatively soft, with a Mohs hardness of 3. The density calculated based on the formula and cell parameters is 2.13 g/cm³. ## History and Name The mineral was named in honor of Frederick Allison Walker (1899–1963), an American chemist and mineral collector from Ann Arbor, Michigan, USA. Walker was known for his specialized collection of borate minerals. Walkerite was approved as a new mineral species by the International Mineralogical Association (IMA) in 2019 (IMA2019-033).

Properties

Mohs hardness: 3
Luster: Vitreous
Streak: White
Density: 2.13
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Transparent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of walkerite is possible almost exclusively through advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). Visual identification in the field or in a collection is practically impossible due to its similarity to many other colorless secondary minerals. ## Distinguishing from Similar Minerals It can be confused with other rare borates, such as gowerite, ulexite, or colemanite, which occur in similar environments. Definitive differentiation requires specialized laboratory tests. ## Crystal Forms Walkerite forms very small, thin, tabular crystals with a hexagonal outline, reaching up to 200 micrometers in size. These crystals often combine into rosette-like or spherulitic (spherical) aggregates.

Geological environment

## Genesis Walkerite is a secondary mineral, crystallizing under low-temperature conditions. It forms in voids and fissures within massive ulexite, within borate deposits of evaporitic origin (formed by the evaporation of saline lakes). ## Mineral Associations This mineral occurs in direct association with ulexite, which is the main component of the host rock. Other associated minerals at the type locality include gypsum and celestine. ## Localities The only known occurrence of walkerite in the world (type locality) is the U.S. Borax open-pit boron mine in Boron, Kern County, California, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" mineral of extreme rarity, every analytically confirmed specimen is exceptionally valuable to specialized collectors and scientific institutions. The most highly prized specimens would be those with well-formed, microscopically visible crystals in the form of rosette aggregates, on a contrasting ulexite matrix. ## Popular Localities The only source of specimens is the U.S. Borax mine in Boron, California. Material from this locality is the only one available on the market, although its circulation is negligible and limited to a narrow circle of specialists.

Care and storage

## Cleaning Due to its extreme rarity and probable fragility, specimens should only be cleaned with compressed air to remove dust. Contact with water and any chemicals should be avoided. ## What to Avoid Avoid contact with water, acids, and other solvents. The mineral is likely sensitive to changes in temperature and humidity. It should not be subjected to ultrasonic cleaning. ## Storage Walkerite specimens should be stored under stable conditions, in a closed, padded "micromount" box, protecting them from dust, moisture, and mechanical damage.

Sources

IMA Mineral List (CNMNC)