ulexite

{{infobox mineral | name = Ulexite | category = Nesoborates | boxwidth = | boxbgcolor =#a49f8d | image = Ulexite-Calcite-40062.jpg | imagesize = 170px | alt = | caption = Ulexite specimen from California | formula = NaCaB5O6(OH)6·5H2O | IMAsymbol = Ulx | molweight = | strunz = 6.EA.25 | dana = 26.05.11.01 | system = Triclinic | class = Pinacoidal () (same H–M symbol) | symmetry = P | unit cell = a = 8.816(3) Å, b = 12.87 Å c = 6.678(1) Å; α = 90.25° β = 109.12°, γ = 105.1°; Z = 2 | color = Colorless to white | colour = | habit = Acicular to fibrous | twinning = Polysynthetic on {010} and {100} | cleavage = Perfect on {010} good on {10} poor on {110} | fracture = Uneven | tenacity = Brittle | mohs = 2.5 | luster = Vitreous; silky or satiny in fibrous aggregates | streak = White | diaphaneity = Transparent to opaque | gravity = 1.95–1.96 | density = | polish = | opticalprop = Biaxial (+) | refractive = nα = 1.491–1.496 nβ = 1.504–1.506 nγ = 1.519–1.520 | birefringence = δ = 0.028 | pleochroism = | 2V = Measured: 73–78° | dispersion = | extinction = | length fast/slow = | fluorescence = Depending on fluorescent impurities, ulexite may fluoresce yellow, greenish yellow, cream, white under short waves and long waves UV | absorption = | melt = | fusibility = | diagnostic = | solubility = Slightly soluble in water | other = Parallel fibrous masses can act as fiber optical light pipes | alteration = | references = }}

Ulexite (), sometimes called TV rock or TV stone due to its unusual optical properties, is a hydrous borate hydroxide of sodium and calcium with the chemical formula . The mineral occurs as silky white rounded crystalline masses or in parallel fibers. Ulexite was named for the German chemist Georg Ludwig Ulex (1811–1883), who first discovered it.