Rhenium Dioxide

Rhenium Dioxide is a reddish brown powder represented by the formula
ReO₂. It is insoluble in water and aqueous alkalis, but it is readily
attacked by oxidizing acids and alkaline hydrogen peroxide solutions to
give the perrhenate ion.

The specific gravity is 11.4 gm/cc. Rhenium Dioxide sublimes at an
estimated temperature of 1363° C (2485° F).