Wilcoxite

Chemical formula: MgAl(S⁶⁺O₄)₂F·₁₈H₂O

Wilcoxite is a very rare, hydrated magnesium aluminum sulfate, forming colorless or white, delicate coatings and efflorescences.

## Characteristics Wilcoxite is a mineral from the sulfate group, chemically classified as a hydrated magnesium aluminum sulfate with an additional fluoride anion. It occurs extremely rarely, forming small, colorless or white coatings, efflorescences, and aggregates of small, bladed crystals. Due to its delicacy and low hardness, wilcoxite specimens are fragile and easily damaged. ## Physical Properties This mineral is characterized by a very low hardness on the Mohs scale, only 1 to 2, which means it can be scratched with a fingernail. Its density is also low, approximately 1.58 g/cm³. Crystals exhibit a vitreous luster and are transparent to translucent. ## Colors and Varieties Wilcoxite is usually colorless or white. No colored or commercial varieties are distinguished. ## History and Name The mineral was first described in 1979. Its name comes from the Wilcox Mining District in Catron County, New Mexico (USA), where its type locality, the Lone Pine mine, is located. This is the only place from which the first described specimens originated. ## Uses Wilcoxite has no industrial applications. Its significance is purely scientific and collectible, as a very rare and unique mineral.

Properties

Mohs hardness: 1-2
Luster: Vitreous
Streak: White
Density: 1.58
Fracture: Conchoidal
Transparency: Transparent,Translucent
Crystal system: Triclinic

Diagnostic features

## Identification Wilcoxite is difficult to identify visually without advanced examination. Its key features include its occurrence as delicate, white or colorless efflorescences and coatings in a specific geological environment. Very low hardness (1-2 on the Mohs scale) and water solubility are important diagnostic clues. ## Distinguishing from Similar Minerals It can be confused with other secondary sulfates such as aubertite, apjohnite, or halotrichite, which form similar efflorescences. Certain differentiation from these minerals requires specialized chemical (EDS) or X-ray (XRD) analyses to confirm composition and crystal structure. ## Crystal Forms It forms aggregates of small, bladed or tabular crystals, as well as delicate, fibrous aggregates, coatings, and efflorescences on the host rock.

Geological environment

## Genesis Wilcoxite is a secondary mineral, formed as a result of weathering processes (oxidation) of sulfides, such as pyrite, in an environment rich in aluminum and magnesium. It forms as a product of post-volcanic activity (fumaroles) or as efflorescences on the walls of old mine workings. ## Mineral Associations This mineral co-occurs with other sulfates and secondary minerals. In its type locality, it was found in association with apertite, magnesite, gypsum, pyrite, and quartz. ## Localities The only confirmed and described locality of wilcoxite in the world is its type locality: the Lone Pine mine in the Wilcox Mining District, Catron County, New Mexico, USA.

Rarity

Very rare

For collectors

## Quality Criteria The quality of a wilcoxite specimen primarily depends on the abundance and development of crystals. The most valued samples are those with visible, even if microscopic, bladed crystals, forming rich coatings on a small fragment of the host rock. Contrast with a darker substrate enhances aesthetic appeal. ## Popular Localities The only source of wilcoxite specimens is its type locality in New Mexico, USA. All samples available on the collector's market come from this single location, making them extremely rare and sought after by specialized systematic mineral collectors.

Care and storage

## Cleaning Wilcoxite specimens are extremely delicate and water-soluble. They should not be cleaned wet. Only very careful dust removal with a soft brush or a stream of compressed air from a distance is permissible. ## What to Avoid Contact with water and other liquids that can dissolve the mineral must be absolutely avoided. It is sensitive to changes in humidity, high temperatures, and mechanical damage due to its extremely low hardness. It should not be exposed to direct sunlight. ## Storage Wilcoxite specimens should be stored under stable conditions, preferably in sealed, closed containers (e.g., "micromount" type) away from sources of moisture and dust. Due to its fragility, vibrations and contact with harder minerals should be avoided.

External references

https://www.mindat.org/min-4288.html