IMPORTANT ELEMENTS AND MINERALS 37 
minerals. While the mineralogist knows more than 
two thousand different kinds, we may omit them all, 
excepting the following nine minerals and groups of 
minerals. Many of those that are omitted are very 
rare, and most would never be seen by the average 
person; but some are of greater consequence, and the 
teacher may deem it worth while to take up their 
study as time permits.’ 
Named approximately in the order of their impor- 
tance, the decidedly common minerals are: (1) quartz; 
(2) the group of feldspars; (3) the group including 
calcite, dolomite, and siderite; (4) the group of micas ; 
(5) the amphibole group; (6) the pyroxene group; 
(7) the group of iron minerals; (8) gypsum; (9) salt ; 
(10) ice and its liquid form, water. The bulk of the 
earth’s crust is made up of these minerals. 
Quartz (silica, SiO,) is the most abundant mineral 
in the crust of the earth. In color, it varies from a 
transparent rock crystal, as clear and pure as plate 
glass, to a jet-black, glassy mass. ‘There are also blue, 
purple, pink, and other colors of quartz. Sometimes 
1 At this point it is hoped that the teacher may see his way to the intro- 
duction of a study of elementary mineralogy, and perhaps to a laboratory 
study of thirty or forty of the most common minerals, so that the student may 
really understand what minerals are, how they vary, and how they may be 
distinguished. Such a study should be introduced from the point of view of 
mineralogy, and each student should study the hardness, color, cleavage, 
specific gravity, crystal form, etc., of each species. Directions for such study 
will be found in any good book on mineralogy. (See also p. 23.) 
