Beryllium Oxide: I*

A bstract This interesting and unusual material forms few mineralogical combinations, although many binary and some ternary diagrams have been plotted. The apparent stable crystalline formation at relatively low temperature has been confirmed by specific‐gravity determinations on the oxide fired at different temperatures and on the electrically fused oxide, both by the writers and others. The thermal expansion of the electrically fused beryllium oxide and of bars of the oxide fired at lower temperatures is also very close. The electrical conductivity is higher than that for magnesia and alumina. The thermal conductivity appears to be greater than that of alumina and zircon. The hardness is 9.