Ulexite

(hydrated sodium calcium borate hydroxide) a.k.a. TV rock, is a mineral occurring in silky white rounded crystalline masses or in parallel fibers. The natural fibers of ulexite conduct light along their long axes, by internal reflection.

White color; silky luster. Mohs hardness 1–2.5, d 1.96. Usually found as rounded, loosetextured masses of fine crystals.

Source of borax.

A natural hydrated borate of sodium and calcium.