What is Ulexite?
Ulexite is a hydrated sodium-calcium borate famous for silky white fibres and the natural fibre-optic effect that can transmit an image through a polished surface.
Mineralogy and structure
Reference formula: NaCaB5O6(OH)6·5H2O. Ulexite is triclinic and highly hydrated. Its parallel fibres can guide light, but the optical effect depends on a polished, well-aligned surface and is not a substitute for mineral identification. The structure image uses exact COD 9000600. Ulexite is classified with borates and has triclinic crystal symmetry. Typical hardness is 2.5–3.5 on the Mohs scale and specific gravity is approximately 1.9–2.0.
Colour, lustre and habit
Typical colours include white, colourless, grey, yellowish. The usual fibrous, radiating, massive habit and silky, vitreous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Ulexite forms in or is associated with evaporite basins, borate lakes, arid playa deposits and volcanic-sedimentary environments. Important documented localities include California and Nevada in the United States, Argentina, Chile, Peru, Turkey and Kazakhstan.
The natural fibre-optic mineral
Ulexite is a strong educational and collector material because its texture explains its optical behaviour. Clean white fibres, an intact satin surface and a documented borate locality make the specimen especially effective.
Collecting and care
Very soft and water-sensitive: keep dry, avoid soaking, abrasion and pressure on fibres, and clean only with a soft dry brush or cloth.
