Rubidium is a chemically reactive, silvery-white metallic element of the alkali metals' group. It is one of the most electropositive and alkaline elements. Rubidium was discovered spectroscopically in 1860 in the mineral lepidolite, which is now the element's main commercial ore. They named the element after the ruby red lines prominent in its spectrum. Metallic rubidium is silvery white and very soft. After cesium, it is the most active of the alkali metals. It tarnishes immediately upon exposure to air and ignites spontaneously to form rubidium oxide. It reacts violently with water.

Rubidium can become liquid at ambient temperature, but only on a hot day given that its melting point is about 40°C. Its flame is yellowish-violet. Rubidium and its salts have few commercial uses. The metal is used in the manufacture of photocells and in the removal of residual gases from vacuum tubes. Rubidium salts are used in glasses and ceramics and in fireworks to give them a purple colour. Potential uses are in ion engines for space vehicles, as working fluid in vapor turbines, and as getter in vacuum tubes.

Rubidium is a widely distributed element, ranking about 16th in order of abundance of the elements in Earth's crust. The relative abundance of rubidium has been reassessed in recent years and it is now suspected of being more plentiful than previously calculated. It is not found in large deposits but occurs in small amounts in certain mineral waters and in many minerals usually associated with other alkali metals. It is also found in small quantities in tea, coffee, tobacco, and other plants, and trace quantities of the element may be required by living organisms. Rubidium is used in making certain catalysts. The rate of radioactive decay of rubidium-87 can be used in geologic age determination.

It is not only like potassium but also there are no environments where it is seen as a threat. No minerals of rubidium are known, but rubidium is present in significant amounts in other minerals such as lepodite (1.5%), pollucite and carnallite. It is also present in traces in trace amounts in other minerals such as zinnwaldite and leucite. The amount of rubidium produced every year is small, and what demand there is can be met from a stock of a mixed carbonate by-product that is collected during the extraction of lithium from lepodite. The little rubidium that is produced is used for research purposes only, these is no incentive to seek commercial outlets for the material.

Rubidium has no known biological role but has a slight stimulatory effect on metabolism, probably because it is like potassium. The two elements are found together in minerals and soils, although potassium is much more abundant than rubidium. Plant will adsorb rubidium quite quickly. When stresses by deficiency of potassium some plants, such as sugar beet, will respond to the addition of rubidium. In this way rubidium enters the food chain and so contributes to a daily intake of between 1 and 5 mg. No negative environmental effects have been reported.

It is moderately toxic by ingestion. If rubidium ignites, it will cause thermal burns. Rubidium readily reacts with skin moisture to form rubidium hydroxide, which causes chemical burns of eyes and skin. Signs and symptoms of overexposure to this element are skin and eye burns, failure to gain weight, ataxia, hyper irritation, skin ulcers, and extreme nervousness. Medical condition is aggravated by exposure to heart patients due to potassium imbalance. In case of exposure to eyes immediately flush with running water for 15 minutes while holding eyelid. Obtain medical attention immediately. In case of skin exposure remove material and flush with soap and water. Remove contaminated clothing. Get medical attention promptly. In case of inhalation move to fresh air immediately. If irritation persists, get medical attention. In case of ingestion do not induce vomiting. Rather try to get medical attention immediately.