Strontium Boride, SrB₆

Strontium Boride, SrB₆, is prepared by heating in the electric furnace a mixture of strontium borate, aluminium, and carbon. The impurities can be readily removed by flotation in bromoform on account of the density of strontium boride. It forms a black crystalline powder, but, when in sufficiently thin layers, it is transparent with a reddish-brown coloration under the microscope. It is harder than quartz, and has a density of 3.28 at 15° C. Its chemical properties are similar to those of calcium boride, but it is slightly less reactive - for example, it is necessary to heat gently in fluorine in order to start the reaction.