Inyoite
Chemical formula: CaB<sub>3</sub>O<sub>3</sub>(OH)<sub>5</sub>·4H<sub>2</sub>O
Inyoite is a hydrated calcium borate, forming large, vitreous crystals that quickly lose water and whiten in the air.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous
- Streak
- White
- Density
- 1.88
- Cleavage
- Perfect on {001}
- Fracture
- Uneven, Conchoidal
- Transparency
- Transparent to Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification A key diagnostic feature of inyoite is its rapid dehydration in dry air, leading to a loss of transparency and the appearance of a white coating. It is also identified by its crystal habit (short-prismatic, tabular), low hardness (2 on the Mohs scale), and vitreous luster on fresh fracture surfaces. ## Distinguishing from Similar Minerals Inyoite is sometimes confused with other colorless, hydrated borates, such as colemanite or meyerhofferite. It is distinguished from colemanite (hardness 4.5) by its significantly lower hardness. Meyerhofferite is a product of its dehydration and usually forms pseudomorphs after inyoite, having a more fibrous character. Selenite (a variety of gypsum) is also very soft but has a different crystal form and perfect cleavage in one direction. ## Crystal Forms Inyoite crystals are monoclinic, most often short-prismatic or thick-tabular. They frequently occur as well-formed, individual crystals grown on a matrix or in vugs filling fissures. They can form radial aggregates.
Geological environment
## Genesis Inyoite is an evaporite mineral. It forms by crystallization from boron-rich waters in closed sedimentary basins (borate lakes) under dry and hot climatic conditions. It forms in playa-type deposits, where seasonal evaporation leads to the precipitation of successive salts. ## Mineral Associations It most commonly co-occurs with other borate minerals, such as meyerhofferite (often as an alteration product), colemanite, hydroboracite, ulexite, as well as with gypsum, calcite, and clay aluminosilicates. ## Localities The most important and classic localities for this mineral are in the USA, in Inyo County, California (Mount Blanco, Gower Gulch, Boraxo mines). It is also known from the Inder Lake region in Kazakhstan, Salta Province in Argentina (e.g., Sijes deposit), and Bigadiç in Turkey.
Rarity
Not very common
For collectors
## Quality Criteria The most prized by collectors are large, fully transparent, colorless crystals with a strong luster and well-developed faces. Specimens that have not undergone the dehydration process (whitening) are significantly more highly valued. Contrastive placement of crystals on a rock matrix also enhances their appeal. Due to the mineral's instability, proper storage is crucial, and specimens preserved in ideal condition for many years fetch higher prices. ## Popular Localities Classic, most sought-after specimens come from historical localities in California, Inyo County. Good quality crystals were also supplied from deposits in Argentina and Kazakhstan.
Care and storage
## Cleaning Inyoite specimens should only be dry-cleaned, using a soft brush or compressed air to remove dust. Contact with water, even distilled water, is highly inadvisable, as it can accelerate the crystal decomposition process. ## What to Avoid Contact with water and other liquids must be strictly avoided. The greatest threat to inyoite is low air humidity, which causes its dehydration and transformation into meyerhofferite, manifesting as dulling and whitening of the surface. It should be protected from direct sunlight and heat sources, which accelerate water loss. It is a very soft and brittle mineral, susceptible to mechanical damage. ## Storage Inyoite requires storage under special conditions. It is best kept in a tightly sealed container (e.g., a membrane box or a sealed box) with a small amount of water (e.g., a water-soaked cotton swab placed nearby, but not touching the specimen) to ensure high relative humidity. Such conditions slow down the dehydration process and help preserve the transparency of the crystals.