What is "rubidium oxide"

n. (context chemistry English) any oxide of rubidium, but especially the yellow solid Rb₂O; it is a strong base, reacting strongly with water to form the hydroxide and with acids to form normal salts

Rubidium oxide is the chemical compound with the formula RbO. Rubidium oxide is highly reactive towards water, and therefore it would not be expected to occur naturally. The rubidium content in minerals is often calculated and quoted in terms of RbO. 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, KLiAl(Al,Si)O(F,OH), wherein Rb sometimes replaces K.

RbO is a yellow colored solid. The related species NaO, KO, and CsO are colorless, pale-yellow, and orange, respectively.

The alkali metal oxides MO (M = Li, Na, K, Rb) crystallise in the antifluorite structure. In the antifluorite motif the positions of the anions and cations are reversed relative to their positions in CaF, with rubidium ions 8 coordinate (cubic) and oxide ions 4 coordinate (tetrahedral).