With all these deformation experiments, it is necessary to scale down as precisely as possible variables such as the time and velocity of the experiment and the viscosity and temperature of the material from the natural to the laboratory conditions.
In the 19th century crystallographers were able to study only the external form of minerals, and it was not until 1895 when the German physicist Wilhelm Conrad Röntgen discovered X-rays that it became possible to consider their internal structure.
For example, the XRF (X-Ray Fluorescence) spectrometer can quantify the major and trace element abundances of many chemical elements in a rock sample down to parts-per-million concentrations.
This geochemical method has been used to differentiate successive stages of igneous rocks in the plate-tectonic cycle.
The oldest known rocks on Earth, estimated at 4.28 billion years old, are the faux amphibolite volcanic deposits of the Nuvvuagittuq greenstone belt in Quebec, Canada.
A radiometric dating technique that measures the ratio of the rare earth elements neodymium and samarium present in a rock sample was used to produce the estimate.
A year later William Bragg of Britain and his son Lawrence perceived that such a pattern reflects the layers of atoms in the crystal structure, and they succeeded in determining for the first time the atomic crystal structure of the mineral halite (sodium chloride).This method has wide applications in, for example, the fields of industrial mineralogy, materials science, igneous geochemistry, and metamorphic petrology.Microscopic fossils, such as ostracods, foraminifera, and pollen grains, are common in sediments of the Mesozoic and Cenozoic eras (from about 251 million years ago to the present).Also, by extrapolating backward in time to a situation when there was no lead that had been produced by radiogenic processes, a figure of about 4.6 billion years is obtained for the minimum age of the Earth.This figure is of the same order as ages obtained for certain meteorites and lunar rocks.Because the rock chips brought up in oil wells are so small, a high-resolution instrument known as a scanning electron microscope had to be developed to study the microfossils.