Kernite, also known as rasorite is a hydrated sodium borate with formula Na 2B 4O 6(OH) 2·3H 2O. 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.
Kernite is soluble in cold water and alters to tincalconite when it dehydrates. It undergoes a non-reversible alteration to metakernite (Na 2B 4O 7·5H 2O) when heated to above 100 °C.