sassolite

{{Infobox mineral | name = Sassolite | category = Borate mineral | boxwidth = | boxbgcolor = | image = Sassolite.jpg | caption = Yellow sassolite | formula = H3BO3 | IMAsymbol = Sso | strunz = 6.AA.05 | system = Triclinic | class = Pinacoidal () (same H-M symbol) | symmetry = P | unit cell = a = 7.02 Å, b = 7.06 Å c = 6.59 Å; α = 103.65° β = 101.11°, γ = 59.98°; Z = 4 | colour = White to gray, may be pale yellow from included sulfur or pale brown from included iron oxides; colourless in transmitted light | habit = As scaly pseudohexagonal crystals; ncrustations; platy; tabular; may be stalactitic | twinning = Around [001] as twin axis, common | cleavage = Perfect on {001}, micaceous | fracture = | tenacity = Sectile | mohs = 1 | lustre = Vitreous to pearly | refractive = nα = 1.340 nβ = 1.456 nγ = 1.459 | opticalprop = Biaxial (−) | birefringence = δ = 0.119 | pleochroism = | 2V = Measured: 5°, Calculated: 16° | streak = White | gravity = 1.46–1.50 |density=1.46-1.50 g/cm3| melt = | fusibility = | diagnostic = | solubility = Soluble in water | diaphaneity = Transparent | other = | references = }}

Sassolite is a borate mineral, specifically the mineral form of boric acid. It is usually white to gray, and colourless in transmitted light. It can also take on a yellow colour from sulfur impurities, or brown from iron oxides.