In the mid-19th century, most elements had been discovered and confirmed by actually extracting them from their compounds chemically. But, chemists were beginning to develop other techniques besides just reacting one chemical with another. Electrolysis was one such tool; English chemist Humphry Davy purified several elements by use of electricity. Another tool was the spectroscope.
As detailed under caesium, around 1850, German chemists Robert Bunsen and Gustav Kirchhoff invented the spectroscope. Elements glow with different characteristic colors or spectra when they are burned. Bunsen's gas flame, now known as the Bunsen burner, was a critical tool for this as it was itself colorless.
Bunsen and Kirchoff used this spectral technique to discover caesium. A year later, in 1861, they saw dark red lines in the mineral lepidolite (right), a kind of mica. This motived them to chemically process 150kg of the mineral and extract a new element for analysis. Bunsen and Kirchoff named it "rubidium" from the Latin rubidus, meaning "deep red".
Mining and Production
Rubidium occurs in several minerals, often with metals that are chemically related, such as potassium. The rubidium that is actually mined is extracted as a byproduct of lithium and caesium mining. Curiously, rubidium is many times more abundant in the earth than either of those metals, yet it has few enough commercial applications that it is not sought after directly. One major source is in Manitoba, Canada. Total worldwide production is not reported, but is probably only a few tonnes per year.
Properties and Uses
Rubidium is a silvery, soft, ductile metal. It is a highly reactive alkali metal with properties similar to the other metals above it in the periodic table. Rubidium reacts with air, with water, and with many of the elements.
Rubidium has the curious property of being very, very slightly radioactive, which puzzled physicists of the early 20th century. One isotope of rubidium is stable, but the other has a half-life of 48 billion years. (The universe is only 14 billion years old.)
The element has only a few uses, and either potassium or cesium will substitute in most cases. It's deep red signature flame is sometimes used in fireworks. Otherwise, it is a popular choice for physics experiments simply because it is a heavy atom with fortuitous properties. Rubidium is therefore hit by lasers, cooled to near absolute zero, and run through magnetic fields.