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A system of dating the ages of rocks.

Rubidium-strontium dating is one of the most widely used techniques in geochronology to date the time of igneous and metamorphic events. In some cases, it is possible to date both an igneous and metamorphic event in the same rocks.

Although Rubidium and Strontium rarely occur in concentrations greater than a few hundred parts per million, they can be found in most rocks.

When a rock forms, it will contain rubidium-87, strontium-87 and strontium-86: as long as nothing is gained or lost from the rock, the amount of rubidium will decrease, and the rate of strontium-87 will increase. Since strontium-86 is not radioactive, its concentration will remain constant.
By measuring the change in concentration of rubidium-87 and strontium-87, it is possible to calculate the age of the rock by using the decay constant.

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