Definitions

Definition of a mineral
A naturally occurring inorganic chemical substance having a definite chemical composition and a characteristic crystal structure.

Definition of a rock
Any naturally occurring solid material composed of one or more minerals and having some degree of chemical and mineralogical constancy.

Therefore, to understand rocks, we need to understand minerals. And, we need to know what the chemical compositions of the minerals are so that we can understand the chemical composition of the rocks. I know that most people should be able to look up the composition of the minerals, but I do have you at least memorize them throughout the semester, so that some of them will become familiar to you. Some things you should know. For example quartz--SiO2.

Mineralogy is the study of minerals: Petrology is the study of rocks.

Although approximately 3500 minerals have been discovered to date, fewer than 40 account for the bulk of the earth’s crust. Because Si and O make up 72.4% of the crust by weight, not surprisingly most rock-forming minerals are silicates.

Examples of different kinds of minerals:

Rock-forming minerals: e.g. quartz, feldspar, and clinopyroxene
Accessory minerals: e.g. Apatite
Ore minerals: chalcopyrite, ilmenite, magnetite, hematite (pyrite)
Industrial minerals: asbestos, diamonds, gravel, potash, salt

Sometimes a mineral can both be rock-forming and/or accessory depending on the rock. For example, biotite is rock-forming in a schist, but may be accessory in a granite.