Geology Reference
In-Depth Information
Realizing Most Rocks Are Built from Silic-
ate Minerals
The minerals commonly found in rocks at the earth's surface are collectively called
rock-
forming minerals.
Of all the known elements, only eight of them make up most of the
rock-forming minerals; these eight elements compose 98 percent of the rocks in the
earth's crust. These eight are:
Oxygen (O)
Silicon (Si)
Aluminum (Al)
Iron (Fe)
Calcium (Ca)
Sodium (Na)
Potassium (K)
Magnesium (Mg)
Silicon and oxygen are the most common elements in the earth's crust. (Refer
back to the pie chart in Figure 2-1, which illustrates the percentage of elements in
earth's crust.) Atoms of these two elements combine to form the basis for a group
of minerals called
silicates.
Every silicate mineral begins with a silicon-oxygen
tet-
rahedron
of atoms like the one illustrated in Figure 6-5. The tetrahedron has four
oxygen atoms attached to a central silicon atom.
Figure 6-5:
The
silicon-oxygen tet-
rahedron.
