NUMBER OF KNOWN MINERALS
Thisis surprisingly small: there are at present about 3,000 known mineral species. Every year several new minerals are described, but, as there are also some which are no longer acceptable as separate minerals because they have been found to be mixtures or fine intergrowths of known species, the number of known and accepted minerals increases but slowly. Compared with the number of chemical compounds, of which there are nearly half a million carbon compounds alone, the number of combinations of elements forming natural minerals is exceedingly small. Even the number of known flowering plant or insect species is many times greater than that of all known minerals.
The term species has been borrowed from the realm of biology, where it has been used to define in a loose way a group of individuals with common characteristics which are able to propagate themselves. As no such criterion can be applied to minerals, the definition of a mineral species is of necessity even more arbitrary than that of an animal or plant species.
RELATIVE ABUNDANCE OF DIFFERENT MINERALS IN THE EARTH’S CRUST. Even more surprising than the small total number of known minerals is their uneven distribution in the earth’s crust.