Editing Rubidium (section)

==Production==
[[File:Die Flammenfärbung des Rubidium.jpg|thumb|upright=0.65|Flame test for rubidium]]

Although rubidium is more abundant in Earth's crust than caesium, the limited applications and the lack of a mineral rich in rubidium limits the production of rubidium compounds to 2 to 4 [[tonne]]s per year.<ref name="USGS" /> Several methods are available for separating potassium, rubidium, and caesium. The [[fractional crystallization (chemistry)|fractional crystallization]] of a rubidium and caesium alum {{chem|(Cs,Rb)Al(SO<sub>4</sub>)<sub>2</sub>·12H<sub>2</sub>O}} yields after 30 subsequent steps pure rubidium alum. Two other methods are reported, the chlorostannate process and the ferrocyanide process.<ref name="USGS" /><ref>{{cite book |url = https://books.google.com/books?id=1ikjAQAAIAAJ&q=ferrocyanide+rubidium |publisher = United States. Bureau of Mines |title = bulletin 585 |date = 1995}}</ref>

For several years in the 1950s and 1960s, a by-product of potassium production called Alkarb was a main source for rubidium. Alkarb contained 21% rubidium, with the rest being potassium and a small amount of caesium.<ref>{{cite journal |title = Cesium and Rubidium Hit Market |journal = Chemical & Engineering News |volume = 37 |issue = 22 |pages = 50–56 |date = 1959 |doi = 10.1021/cen-v037n022.p050}}</ref> Today the largest producers of caesium produce rubidium as a by-product from pollucite.<ref name="USGS" />