Re: How do rocks differ from minerals and three examples.

Allison -

My introductory geology text defines a mineral as any naturally formed, solid chemical element or compound with a definite composition and a characteristic crystal structure. Any uniform crystal counts as a mineral. Diamond, feldspar, quartz and calcite are all minerals. Rock on the other hand is any naturally formed, nonliving, firm mass of solid matter. Most rocks are made up of collection of minerals. Some rocks like limestone, are made up mostly of one type of mineral (calcite, CaCO3) while others can be a mix of many different sorts of minerals: granite and gabbro are good examples. If you look at most granite, you can see the individual grains of the different minerals that make it up. Not all rocks are made up of minerals, however. Obsidian (a natural type of glass) is made up of silicon and oxygen but doesn't have a characteristic structure so it isn't a mineral. Coal is a rock made out of fossilized organic matter, not minerals. These are the exceptions to the rule- most rocks are made up of minerals. If you have any questions, feel free to e-mail me.

Alex Barron

Source:
B.J. Skinner and S.C. Porter. The Blue Planet. John Wiley and Sons. 1995.