Rock form in a variety of geologic setting ranging from locations on or near the earth surface, deep underground, or even in outer space.
Most of the rocks we see on the surface of the planet formed by processes that happened long ago, but we can see these processes actively taking place in many places.
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus.
Common examples of elements are iron, copper, silver, gold, hydrogen, carbon, nitrogen, and oxygen.
In "nature,"here are at least 254 stable isotopes that have never been observed to decay.
Rocks are composed of particles ranging from microscopic grains to full sized crystals and crystal grains of different kinds of minerals, and containing many different identifiable physical characteristics.Everything around us is made of chemical compounds that have testable and identifying characteristics, allowing them to be classified, and their age determined.This also applies to rocks, minerals, and derivative materials (such as sediments and soil).It is conceptually important that each rock has an origin in concepts of place, time, and physical and chemical conditions. These changes may be rapid (such as a volcanic explosion) or gradual, taking place over millions or billions of years, and involving movement over great distances, both at the surface or to deep within the Earth's crust below us.Trying to explain the what, how, and when of a rock's journey is fundamental to explaining why rocks are significant to resolving questions about our Earth's history and conditions within the physical environments where we live.In contrast, minerals considered "gems" are, mostly, exceedingly rare.A rock is a relatively hard, naturally formed mineral or petrified matter; a naturally formed aggregate of mineral matter constituting a significant part of the earth's crust.For instance, rocks and minerals formed deep underground may not be stable in the surface environment where they are exposed to water, air, temperature changes, and other physical and chemical conditions.All matter is made up of atoms, and atoms are made up of atomic particles (electrons, protons, and neutrons - see Figure 2-5).The lightest element, hydrogen, has one proton, whereas the heaviest naturally occurring element, uranium, has 92 protons. Isotopes are each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties.Some isotopes are not stable and ultimately break down or change in other elements.