Absolute dating on rocks

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Each of these minerals has a different initial rubidium/strontium ratio dependent on their potassium content, the concentration of Rb and K in the melt and the temperature at which the minerals formed.

Rubidium substitutes for potassium within the lattice of minerals at a rate proportional to its concentration within the melt.

The age of a sample is determined by analysing several minerals within the sample. If these form a straight line then the samples are consistent, and the age probably reliable.

The slope of the line dictates the age of the sample.

In addition, Rb is a highly incompatible element that, during partial melting of the mantle, prefers to join the magmatic melt rather than remain in mantle minerals. The radiogenic daughter, Sr, is produced in this decay process and was produced in rounds of stellar nucleosynthesis predating the creation of the Solar System.

Different minerals in a given geologic setting can acquire distinctly different ratios of radiogenic strontium-87 to naturally occurring strontium-86 (Sr as the parent melt.

During fractional crystallization, Sr tends to become concentrated in plagioclase, leaving Rb in the liquid phase.

Marble, granite, and quartz are valued for their uses in making statues and buildings, Sand and gravel are commonly used for concrete and road building.

These printables describe the rock cycle, the different types of rocks, and the ways people use rocks and minerals.

Thus, assigning age significance to a result requires studying the metasomatic and thermal history of the rock, any metamorphic events, and any evidence of fluid movement.

A Rb-Sr date which is at variance with other geochronometers may not be useless, it may be providing data on an event which is not representing the age of formation of the rock.

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