IMPORTANT ELEMENTS AND MINERALS 30 
slowly evaporate, distinct cubes begin to form; and as 
they grow in size, they still remain cubes. These are 
crystals’ (Figs. 3, 5, 6, and 10), a crystal being a 
chemically homogeneous solid, bounded by plane faces, 
Hig. 3: 
A group of five perfect crystals. Upper one, garnet; middle, staurolite; lower, 
zircon; left hand, iron pyrite; right hand, chalcopyrite. 
which make certain definite angles with each other, 
depending on the peculiar internal structure of the 
substance. 
Usually minerals form under conditions, such as a 
1 Crystals are also formed by chemical change in many substances which 
are not technically minerals, but are artificially produced. However, the 
laws operating, and the results reached, are the same in both cases. 
