Kernite, also known as rasorite, is a hydrated sodium borate hydroxide mineral with formula Na2B4O6(OH)2·3H2O.

It is relatively soft with Mohs hardness of 2.5 to 3 and light with a specific gravity of 1.91.

Kernite is soluble in cold water and alters to tincalconite when it dehydrates.

This type material is stored at Harvard University, Cambridge, Massachusetts, and the National Museum of Natural History, Washington, D.C.[3] The Kern County mine was the only known source of the mineral for a period of time.

[3] The largest documented, single crystal of kernite measured 2.44 x 0.9 x 0.9 m3 and weighed ~3.8 tons.