Rubidium oxide

Rubidium oxide is highly reactive towards water, and therefore it would not be expected to occur naturally.

In reality, the rubidium is typically present as a component of (actually, an impurity in) silicate or aluminosilicate.

A major source of rubidium is lepidolite, KLi2Al(Al,Si)3O10(F,OH)2, wherein Rb sometimes replaces K. Rb2O is a yellow colored solid.

The alkali metal oxides M2O (M = Li, Na, K, Rb) crystallise in the antifluorite structure.

The tarnishing process is relatively colorful as it proceeds via bronze-colored Rb6O and copper-colored Rb9O2.

NFPA 704 four-colored diamond Health 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gas Flammability 0: Will not burn. E.g. water Instability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calcium Special hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid