MINERALS AND MINERALOGY 



3817 



MINERALS AND MINERALOGY 



Salt, a mineral by crystallization. A cup of 

 water, in which has been placed a quantity of 

 salt, will show how the great salt deposits in 

 various parts of the earth have been formed. 

 When all the salt that will dissolve has been 

 put in water, the solution is said to be satu- 

 rated; that is, the water will take up no more 

 salt. If this cup of salt solution is placed in 

 the open air the water will slowly evaporate, 

 and little crystals of salt will form on the sides 

 of the dish. When the water is completely 

 evaporated, tiny salt crystals will be found on 

 the bottom and sides of the dish. In this 

 manner soda, borax and rock salt deposits are 

 formed; these minerals were once in solution 

 in the water of ponds and lakes, and when the 

 water, for one reason or another, dried up or 

 changed its position, the mineral deposits, more 

 or less mixed with mud, were left on the bot- 

 tom. Most of the great iron deposits were 

 formed in a similar way, although usually the 

 bogs or beds of liquid were slowly subjected 

 to great pressure and underwent a change to 

 the crystalline form. 



Salt and many other minerals were once dis- 

 solved in water deep down in the earth. Some- 

 times the water was hot, a condition sufficient 

 to cause solution, and often it held a number 

 of minerals which acted on each other to pre- 

 serve the solution. In the course of ages the 

 water was forced upward toward the surface 

 of the earth and gradually became cooler. The 

 pressure on it became less, and little by little 

 the minerals which it had carried in suspense 

 were deposited. As these deposits dried and 

 hardened, veins of quartz, calcite, gypsum, gold 

 and other minerals were formed. The many 

 mineral springs which are still flowing in every 

 part of the earth show us how these veins were 

 formed centuries ago. 



Sulphur, a mineral by condensation. A few 

 minerals seem to have existed in the earth's 

 interior in the form of vapor or gas. As this 

 vapor found its way toward the surface, it was 

 cooled and condensed on the walls of the 

 cracks in the earth's crust. Here it is often 

 mixed with other minerals, such as iron pyrites, 

 but it is also found in the pure state. This 

 method may be illustrated by a simple experi- 

 ment which any parent or teacher can conduct. 

 Take a little sulphur and place it in a glass 

 tube closed at one end. If the sulphur is 

 heated over the flame of a lamp, it will soon 

 begin to change to a brownish-yellow vapor. 

 The vapor will rise in the tube, and when it 

 reaches a cool part will condense on the sides. 



The upper part of the tube will be covered 

 with little yellow specks. 



Quartz, feldspar and other igneous minerals. 

 Igneous fusion is the third method by which 

 minerals were formed. This means that a 

 great mass of mineral matter was once heated 

 (ignis is the Latin for fire) to a fluid condition. 

 As the fluid slowly cooled the different elements 

 grouped themselves according to their chem- 

 ical attractions, or likes and dislikes, as they 

 might be called. Molecules of feldspar will 

 form and attract others; molecules of horn- 

 blende, of quartz and other minerals will do 

 the same. When the whole mass is finally 

 cooled there will be distinct smaller masses of 

 each mineral. If, however, the molten mixture 

 cools rapidly, the molecules of the different 

 molecules will not have time to group them- 

 selves, and they will form a mass like obsidian, 

 or volcanic glass. 



Characteristics of Minerals. No matter 

 where or how a certain mineral may have 

 formed, its characteristics are nearly always 

 the same. Quartz always tends to assume cer- 

 tain geometrical forms. Its hardness, specific 

 gravity, luster and the way it conducts light 

 and heat are about the same in all specimens, 

 no matter whether they have crystallized from 

 a lava or from waters underground. To a cer- 

 tain degree, the characteristics of a mineral 

 depend upon the element or elements which it 

 contains, but other less-known factors also 

 contribute to the individuality of a mineral. 

 Graphite and diamond are both pure, carbon; 

 one is soft, the other hard. Graphite is black 

 and greasy; the diamond is transparent and 

 sparkling. Copper when pure is reddish and 

 metallic. Malachite, a combination of copper, 

 carbon 'dioxide and water, is green. Azurite, 

 which has the same ingredients as malachite, 

 but in different proportions, is blue. Both 

 malachite and azurite, unlike native copper, 

 are nonmetallic. The study of the characteris- 

 tics of minerals is one of the principal functions 

 of mineralogy. 



Mineralogy, the Science of Minerals. In ad- 

 dition to the study of the origin and occurrence 

 of minerals and their classification, mineralogy 

 treats of the characteristics of minerals. These 

 may be divided into three kinds the morpho- 

 logical, the physical and the chemical charac- 

 ters; these are discussed below. 



Crystallography. This branch is morphol- 

 ogy, that is, the study of form. Crystallog- 

 raphy includes the description of crystals, their 

 character and classification, besides the methods 



