To which mineral group do most of the rocks in earths crust belong?

Silicates

Explanation:

About 90 percent of the earth's crust is composed from silicate class of minerals. They are the various compounds of silicon and other chemical elements. Quartz and feldspar are the two most common types of silicate types that are found in Earth’s crust. Mica and olivine, which are the lesser concentrates of silicates are also found abundantly in the earth's crust.

c-14 is carbon-14, or radiocarbon.   it is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.