Celestite: SrSO4, Strontium Sulfate

Identification of
Rock Forming Minerals

Minerals are the natural material that every inorganic material on planet Earth is composed of. They are the foundation of both our planet and most human industry.

Minerals can be defined as naturally occurring, inorganic substances that have characteristic chemical composition. Because individual minerals must have the same chemical composition, they must also share distinctive physical properties and have a crystalline atomic structure. This means that the atoms or molecules that make up each mineral exist in an orderly three dimensional arrangement. The structure that results from such arrangement is called a crystal.

Seven properties are commonly used to identify minerals: color, luster, hardness, streak, cleavage, fracture, and crystal form. For many of the minerals you will look at, these properties will be all that is necessary to identify the samples. However, at times other properties such as reaction to acid, magnetism, striation, and the existence of exsolution lamellae will be needed to make a correct identification.

To begin identifying minerals you will first have to determine the mineral's luster.  The luster of a mineral is a description of how a mineral reflects light. This can be described by either a metallic luster or a nonmetallic luster. If a mineral has a metallic luster, it will appear to have a silvery, gold, brassy, or iron look it. Nonmetallic minerals will appear more earthy or glassy. When observing luster, it is important to observe a freshly broken surface of the mineral since oxidation can occur on exposed surfaces and the mineral will become tarnished.

Once you have determined the minerals luster click on the appropriate link in the menu on the left.