Rubidium is the second most electropositive of the non-radioactive alkali elements and melts at a temperature of 39.3 °C (102.7 °F). Like other group 1 elements, this metal reacts violently with water. As with potassium (which is slightly less reactive) and cesium (which is slightly more reactive), this reaction is usually vigorous enough to ignite the hydrogen gas it liberates. Rubidium has also been reported to ignite spontaneously in air. Like other alkali metals, it forms amalgams with mercury and it can form alloys with gold, cesium, sodium, and potassium. The element and its ions give a reddish-violet color to a flame. It was named after two strong emission lines in the dark red area of the spectrum.
As a symmetrical effect of rubidium metal's high reactivity toward oxidation and tendency to subsequent formation of the rubidium cation Rb+, this cation, once formed, is very stable, and is normally unreactive toward further oxidative or reductive chemical reactions.
Rubidium is about the twenty-third most abundant element in the Earth's crust, roughly as abundant as zinc and rather more common than copper. It occurs naturally in the minerals leucite, pollucite, carnallite and zinnwaldite, which contain up to 1% of its oxide. Lepidolite contains between 0.3% and 3.5% rubidium and this is the commercial source of the element. Some potassium minerals andpotassium chlorides also contain the element in commercially significant amounts.
Uses and Application
Rubidium-rich feldspars are used in ceramics applications for spark plugs and electrical insulators because of their high dielectric capacity. Rubidium is also used in specialty glasses, photoelectric cells, and in vacuum tubes.
Rubidium is primarily produced as by-products or co-products with other pegmatite minerals. Demand is limited by the lack of availability of supply. Annual consumption consists of about 200 tonnes derived from lepidolite and 60,000 tonnes of Rb-feldspar concentrate. Recent price quotations are $(US) 800.00/tonne for lepidolite and $(US) 80.00-125.00/tonne for Rb-feldspars.