Sassolite is a boratemineral, and is the mineral form of boric acid. It occurs in volcanicfumaroles and hot springs, as well as in bedded sedimentary borate deposits. Its mineral form was first noted in the early 19th century, and was named after Sasso, Italy, where it was found. Usually coloured white to gray, it is colourless in transmitted light, and can also take on a yellow colour from sulfur impurities, or brown from iron oxides.
See the boric acid entry for additional information.