Danburite
Danburite is a calcium boron silicate mineral with a chemical formula of CaB2(SiO4)2.
It has a Mohs hardness of 7 to 7.5 and a specific gravity of 3.0. The mineral has an orthorhombic crystal form. It is usually colourless, like quartz, but can also be either pale yellow or yellowish-brown. It typically occurs in contact metamorphic rocks.