To be classified as a "true" mineral, a substance must be a solid and have a crystal structure. It must also be an inorganic, naturally-occurring, homogeneous substance with a defined chemical composition. The chemical composition may vary between end members of a mineral system. For example the plagioclasefeldspars comprise a continuous series from sodium-rich albite (NaAlSi3O8) to calcium-rich anorthite (CaAl2Si2O8) with four recognized intermediate compositions between. Mineral-like substances that don't strictly meet the definition are sometimes classified as mineraloids. Other natural-occurring substances are Nonminerals. Industrial minerals is a market term and refers to commercially valuable mined materials (see also Minerals and Rocks section below).
A crystal structure is the orderly geometric spatial arrangement of atoms in the internal structure of a mineral. There are 14 basic crystal lattice arrangements of atoms in three dimensions, and these are referred to as the 14 "Bravais lattices". Each of these lattices can be classified into one of the six crystal systems, and all crystal structures currently recognized fit in one Bravais lattice and one crystal system. This crystal structure is based on regular internal atomic or ionic arrangement that is often expressed in the geometric form that the crystal takes. Even when the mineral grains are too small to see or are irregularly shaped, the underlying crystal structure is always periodic, and can be determined by X-ray diffraction.
Chemistry and crystal structure together define a mineral. In fact, two or more minerals may have the same chemical composition, but differ in crystal structure (these are known as polymorphs). For example, pyrite and marcasite are both iron sulfide, but their arrangement of atoms differs. Similarly, some minerals have different chemical compositions, but the same crystal structure: for example, halite (made from sodium and chlorine), galena (made from lead and sulfur) and periclase (made from magnesium and oxygen) all share the same cubic crystal structure.
Check out the Vet Gazette Thu, 25 Jun 2009 00:00:00 -0700 Stay up-to-date with the College of Veterinary Medicine with the Vet Gazette. What Makes a Happy Cow? Tue, 19 May 2009 00:00:00 -0700 Oregon State University dairy cows are sporting a fashionable new orange accessorythat is designed to gather a variety of information on the cows' movements, which will allow researchers to learn which conditions, including food, surroundings and density of cows put together, make them the happiest. <img class="thumb" src="http://oregonstate.edu/enewsletter/images/happycow.jpg" alt="Photo of Cow" title="OSU Makes Cows Happy" /> Check out the Vet Gazette Tue, 19 May 2009 00:00:00 -0700 Stay up-to-date on news in the College of Veterinary Medicine! Pet Day 2009 is Coming! Fri, 17 Apr 2009 00:00:00 -0700 Oregon State's College of Veterinary Medicine is pleased to host its 22nd annual Pet Day and Open House on May 2. Check it out! <img class="thumb" src="http://oregonstate.edu/enewsletter/images/petday2009.jpg" alt="Pet Day logo" title="College of Veterinary Medicine hosts Pet Day" /> Oregon State Researchers Monitoring Potential Spread of Fungal Disease Tue, 17 Mar 2009 00:00:00 -0700 A fungal organism called Cryptococcus gattii, which caused a disease outbreak among humans and animals on Vancouver Island 10 years ago, may be showing signs of emerging in other areas of the Pacific Northwest, including Oregon, say pathologists at OSU. OSU Researcher to Work with Marion County Youths on Vet Med Project Wed, 18 Feb 2009 00:00:00 -0800 Elementary students at Marion and Turner schools in Marion County will have the opportunity to learn about the intestinal physiology of a llama, examine a freeze-dried horse leg, compare the differences between a veterinarian and a medical doctor, and help conduct an exam on a dog.