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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).










This sample of realgar in clay was taken from Northern Nevada, where it is quite common.
THE MINERAL REALGAR, IS COMPOSED OF THE ELEMENTS OF ARSENIC AND SULFUR. IT IS A MAJOR SOURCE OF ARSENIC.

Realgar is monochlinic, has a hardness of 1.5 to 2 mhos, SG of 3.5, is red, yellow and orange-yellow. Is associated with silver, antomony, and orpiment. It is dieesminated in clay and dolomite. It is used in fireworks and in pigments. The mineral is of little economic value.

Arsenic is a metallic chemical element in Group VA of the periodic table. Its symbol is As, its atomic number 33, and its atomic weight 74.9216. The Earth's crust contains only about 5.5 parts arsenic per million. Arsenic occurs in numerous minerals, in particular realgar, orpiment, and arsenopyrite. Arsenic and some arsenic compounds have been known for a long time. Aristotle thought that arsenic was a kind of sulfur. In about 1250, Albertus Magnus became the first to describe a method of manufacturing arsenic. Since then the method has scarcely changed: the mineral arsenopyrite is heated and decomposes with the liberation of arsenic gas. The gas can be condensed on a cold surface.
 

This sample of realgar in clay was taken from Northern Nevada, where it is quite common. The Realgar is the red portion.



This sample of realgar in clay was taken from Northern Nevada, where it is quite common.