A mineral is a naturally occuring, homogeneous, solid with a crystalline atomic structure. Crystallinity implies that a mineral has a definite and limited range of composition, and that the composition is expressible as a chemical formula. Some definitions of minerals give them as inorganic materials, however both diamonds and graphite are considered minerals, and both are primarily comprised of carbon, which would make them organic. So this leads me, as an engineer, to believe that mineralogists do not have a good, precise definition of a mineral, but rather a loose definition. The definition above, is the most inclusive and would include all substances currently described as minerals. The key items that make something a mineral are occurring naturally, and the definite crystal structure, that is expressible as a chemical formula. Rocks that do not meet this criteria are referred to as amorphis - not having a definite structure or expressible as a chemical formula. Some elements that occur naturally and are minerals are arsenic, bismuth, platinum, gold, silver, copper, and sulphur.

THE DEFINITION OF ORGANIC: Organic chemistry is the study of those substances containing carbon in combination with hydrogen (H), and a few other non metals, namely oxygen (O), nitrogen (N), sulfur (S) and the halogens (F2, Cl2, Br2, and I2).

Feldspars are the most abundant and widespread minerals of the crust, or outermost part, of the Earth. Because of their abundance, feldspars are used in the classification of IGNEOUS ROCKS. They are also abundant in METAMORPHIC ROCKS and in some sediments and SEDIMENTARY ROCKS, especially those formed in arid and semiarid regions. Feldspars are also major constituents of moon rocks, which are similar to rocks of the Earth's crust. Feldspars are used in the manufacture of ceramics and ceramic glazes and as mild abrasives. A few varieties, including labradorite and orthoclase, are occasionally used as gems because they show an iridescent play of colors or a milky translucence. Milky varieties are termed moonstone.

Feldspars are aluminosilicates, containing silicon and aluminum ions bound together by oxygen ions to form a three-dimensional framework of atoms. Other ions, principally potassium, sodium, and calcium, occupy sites within the framework and give rise to the three pure, or end-member species: orthoclase, albite, and anorthite. Feldspars are slightly translucent and have a glassy, or vitreous, luster rather like that of glazed porcelain. Because their atomic framework has planes of weakness, feldspars exhibit good cleavage, breaking readily into blocky pieces with smooth sides. On the Mohs mineral hardness scale, feldspars are 6--slightly harder than a steel knife blade and about as hard as porcelain.