MINERALS AND MINERALOGY 



3816 



MINERALS AND MINERALOGY 



includes all forms of animal and plant life; the 

 second division includes all minerals. 



What Is a Mineral? Animals and plants 

 have their beginning; they grow up, and they 

 die after a longer or shorter existence. Ani- 

 mals have organs, which they use for eating, 

 drinking, breathing and other purposes. Most 

 animals are able to move from place to place, 

 and even those which are unable to move about 

 the coral, for example are able to move 

 parts of their bodies. Plants are simpler in 

 structure than animals, yet they, too, have 

 organs for various purposes. Minerals, on the 

 other hand, have no organs, and show no signs 

 'of life. A mineral does not grow by assimilat- 

 ing food, but by additions from the outside. 

 A piece of mineral may be broken into a dozen 

 pieces, but each piece is exactly as much a 

 mineral as before. In an animal or plant, how- 

 ever, each part has a special purpose, and it is 

 maimed or destroyed if it is cut into pieces. 



This difference between minerals and animals 

 or plants can be expressed in a more scientific 

 way by saying that a mineral is homogeneous; 

 in other words, every part of it is like every 

 other part. An animal is composed of bones, 

 flesh, blood, skin, hair or fur and the like, 

 whereas a mineral is only one thing. A gold 

 nugget is only gold, and every part of it is gold. 

 This does not mean that a mineral cannot be 

 divided into its components. On the contrary, 

 one of the essentials of a mineral is that it 

 has a definite composition which may always 

 be expressed by the same chemical formula. 

 Every mineral is composed of one or more ele- 

 ments, usually two, in a fixed proportion. See 

 CHEMISTRY, subhead Elements. 



A mineral, strictly defined, is a "substance 

 of definite chemical composition which has 

 been directly produced by the processes of in- 

 organic nature." Products of the laboratory or 

 furnace are not minerals, although they may be 

 similar to them. Coal, which is a vegetable 

 product, is not a true mineral, but it is usually 

 treated as one for convenience because it is 

 formed like a mineral and has many of the 

 characteristics of minerals. With the exception 

 of water and mercury (quicksilver) all miner- 

 als, in their normal state, are solids. 



Difference between Minerals and Rocks. Min- 

 erals, it is understood, are elements in chemical 

 combination. Hocks are large masses of miner- 

 als in physical or mechanical combination. A 

 few rocks, to be sure, are composed of only one 

 mineral; marble is one of these. But most 

 rocks are composed of a mixture of two or more 



minerals, and these minerals are not always 

 present in the same proportion. A lump of 

 granite contains quartz, feldspar and mica; it 

 is still granite whether there is little mica, or 

 much, whether there is little quartz or whether 

 quartz forms half the rock. In a piece of gran- 

 ite, the mica is there as mica, the feldspar as 

 feldspar, and the quartz as quartz. If a piece 

 of granite is crushed to fine bits, the pieces will 

 be pieces of mica, feldspar and quartz, not of 

 granite. A mineral, when it is pure, always 

 has the same weight per unit of measure. The 

 weight of a rock, such as granite, varies with 

 the percentage of minerals composing it. A 

 rock has no particular form or color; these 

 characteristics depend on the minerals of which 

 it is composed. 



Distinction between Metallic and Nonmetal- 

 lic Minerals. Minerals may be divided into 

 two classes, metallic and nonmetallic. The 

 metallic minerals are opaque and usually have 

 a shining appearance, or metallic luster. When 

 polished they reflect light like a mirror. As a 

 rule metallic minerals are heavy. From them 

 is extracted most of the gold, lead, silver, iron, 

 tin and zinc of commerce. The nonmetallic 

 minerals are transparent, at least on thin edges. 

 Many are glassy in appearance. Most of them 

 are not heavy. Gold, silver and hematite are 

 metallic minerals. Quartz, feldspar and calcite 

 are nonmetallic. Most of the minerals com- 

 posed of but one element are metallic, but sul- 

 phur and the diamond are exceptions. The 

 majority of metallic minerals are compounds 

 of two or more elements. Such are galena, the 

 ore of lead, and chalcocite, the dark copper ore. 

 A few minerals, such as the dark mica, are me- 

 tallic in appearance, but are transparent and in 

 other ways are unlike metallic minerals. They 

 are called submetallic. 



Origin and Formation of Mineral Deposits. 

 It is now generally believed by scientists that 

 the interior of the earth is not hollow, but is 

 composed of great masses of minerals. Just 

 how the minerals reached the surface nobody 

 knows, but from natural processes which 

 be seen in operation to-day scientists res 

 by analogy about the past. Almost all of the 

 important minerals, moreover, have been 

 cessfully produced artificially, and the infor- 

 mation gained by experiment has thrown con- 

 siderable light on the formation of natural min- 

 erals. All minerals, apparently, once existed in 

 a fluid or molten state, and became solids ii 

 one of three ways. Each of these ways is best 

 understood from an example. 



