Rubidium nitrate

 Rubidium nitrate is a white crystalline powder that is highly soluble in water and very slightly soluble in acetone. In a flame test, RbNO3 gives a mauveght purple colour. 

Rubidium compounds have very few applications.[1] Like caesium nitrate, it is used in infrared radiation producing pyrotechnic compositions as a colorant and an oxidizer, e.g. in decoys and illumination flares. It is also used as a raw material for preparation of other rubidium compounds and rubidium metal, for manufacture of catalysts and in scintillation counters. It is rarely used in fireworks to produce a red-violet color.