So we expect that the description of the velocities of molecules in a gas will in fact be the most probable distribution, since we are dealing with particle numbers in the range of Avogadro's number. But this most probable distribution (the Maxwell-Boltzmann distribution) is subject to constraints, namely that the number of particles is constant and that the total energy is constant (conservation of energy).
The oldest rocks are metamorphic gneisses which are to be found on Inishtrahull, several miles off Malin Head in Co. Donegal, and elsewhere in the north-west. They originally formed as igneous rocks 1750-1780 million years ago.
The word igneous comes from the Latin for fire, and what igneous rocks have in common is that they formed by the cooling and crystallization of a melt. This material may have been lava erupted at the Earth's surface, or magma (unerupted lava) at depths of up to a few kilometers, or magma in deeper bodies (plutons).ranite is the light, coarse-grained rock formed at depth and exposed after deep erosion. It is rich in feldspar and quartz (silica) and hence is called a felsic rock. So granite is felsic and plutonic. Basalt and granite account for the great majority of igneous rocks.