Kernite, also known as rasorite is a hydrated sodium borate hydroxide mineral with formula Na₂B₄O₆(OH)₂·3(H₂O). It is a colorless to white mineral crystallizing in the monoclinic crystal system typically occurring as prismatic to acicular crystals or granular masses. It is relatively soft with Mohs hardness of 2.5 to 3 and light with a specific gravity of 1.91. It exhibits perfect cleavage and a brittle fracture.