Borax

Chemical formula: Na₂B₄O₅(OH)₄·₈H₂O

Borax is a hydrated sodium borate that forms unstable, colorless or white crystals, which easily lose water and transform into tincalconite.

## Characteristics Borax, also known as tincal, is a mineral from the borate group. It forms large, but often poorly developed, prismatic crystals. It usually occurs as granular, earthy aggregates or as efflorescences on rock surfaces. Fresh specimens are colorless or white and transparent, but in dry air, they quickly dehydrate. During this process, they lose their water of crystallization, becoming white, opaque, and brittle, and their surface becomes covered with a powder of tincalconite mineral. ## Physical Properties Borax is a very soft mineral, with a hardness of only 2-2.5 on the Mohs scale, which means it can be scratched with a fingernail. It has a vitreous luster, and an earthy luster on weathered surfaces. It is light, with a density of about 1.7 g/cm³. Characteristic features include its sweetish-alkaline taste and solubility in water. ## Colors and Varieties Most often, it is colorless, white, or grayish. Impurities can give it yellowish, greenish, or even bluish hues. There are no distinct color varieties or commercial varieties; the name "tincal" is a historical synonym used mainly in reference to raw material from Asian deposits. ## History and Name The name "borax" comes from the Arabic word *buraq* or Persian *burah*, meaning "white," which refers to the color of the mineral. It has been known since antiquity and was transported from Tibet to Europe as early as the Middle Ages. As a distinct mineral, it was described in 1748 by Johan Gottschalk Wallérius. ## Uses Borax is the main source of boron. It has wide applications in the chemical industry for the production of boric acid, glass (including borosilicate glass, e.g., Pyrex), ceramics, enamels, and glazes. It is also used as a flux in metallurgy, a cleaning agent, an antiseptic, a wood preservative, and as a component of fertilizers.

Properties

Mohs hardness: 2-2.5
Luster: Vitreous, Resinous, Greasy, Earthy
Streak: White
Density: 1.7-1.72
Cleavage: Perfect on {100}, good on {110}, poor on {010}
Fracture: Conchoidal
Transparency: Transparent to translucent, Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Key diagnostic features of borax include its low hardness (2-2.5), solubility in water, sweetish-alkaline taste, and rapid dehydration in dry air, leading to the formation of a white, powdery tincalconite coating. Crystals often have a characteristic, short, prismatic shape. ## Distinguishing from Similar Minerals Borax can be confused with other evaporites, such as halite, kernite, or colemanite. - **Halite** has a salty taste and excellent, three-directional cleavage (cubic). - **Kernite** is harder (hardness 3) and forms elongated, often splintery aggregates. - **Colemanite** is much harder (4.5) and does not dissolve as easily in water. - **Tincalconite**, a dehydration product of borax, is powdery and has a different crystal shape (octahedra). ## Crystal Forms Borax crystallizes in the monoclinic system, forming short, prismatic crystals with a hexagonal cross-section. They are often flattened. It also occurs in granular, massive aggregates, as well as efflorescences and crusts.

Geological environment

## Genesis Borax is an evaporite mineral. It forms as a result of the evaporation of saline lake waters (so-called playas) and drying sedimentary basins in dry, desert climates. It crystallizes directly from waters rich in boron, sodium, and other salts. It is a typical seasonal mineral that can dissolve and recrystallize depending on the time of year. ## Mineral Associations It most commonly co-occurs with other borates and evaporites, such as halite, kernite, colemanite, ulexite, as well as sulfates (thenardite, mirabilite) and carbonates (trona, nahcolite). ## Localities The most important and well-known borax deposits in the world are located in the United States, in California (Searles Lake, Boron, Death Valley) and Nevada. Large deposits also occur in Turkey (Kirka), Tibet (China), Argentina, Bolivia, and Chile. Many of these localities are dried lake beds.

Rarity

Not very common

For collectors

## Quality Criteria Large, well-formed, transparent, and undamaged borax crystals are most valued by collectors. Since the mineral is very unstable, specimens that have retained their original form, transparency, and luster are significantly more valuable. Specimens from classic, historical localities, such as Searles Lake, are also of great interest. Due to the difficulties in preservation, high-quality borax is rare in collections. ## Popular Localities The most famous collector specimens come from the U.S. Borax mine in Boron and from Searles Lake in San Bernardino County, California, USA. Large, classic crystals were obtained from these locations. Deposits in Tibet also hold historical significance.

Care and storage

## Cleaning Borax is very sensitive to water and changes in humidity. It should absolutely not be washed in water, as it will dissolve. To remove dust, a very soft, dry brush or compressed air from a safe distance can be used. ## What to Avoid Avoid contact with water and any liquids. The mineral is very sensitive to dry air, which causes its rapid dehydration and disintegration (transformation into tincalconite). It should be protected from direct sunlight and heat sources, which accelerate this process. It is extremely unstable under household conditions. ## Storage Borax specimens require special conditions. They are best stored in tightly sealed containers (e.g., "perky box" type) or zip-lock bags to maintain stable, elevated humidity. A small cotton swab soaked in water (but not touching the specimen) can be placed in the container to prevent drying out. Display should be in sealed display cases with controlled humidity.