2) Rocks and Minerals (Appendix 2 and handout)

Mineral: a naturally occurring inorganic crystalline solid with a fixed chemical composition.

1. Naturally occurring: Not man made.

2. Inorganic: not related to hydrocarbons or biological chemicals.

3. Crystalline: A minerals constituent atoms are arranged in a regular and repeating pattern.

4. Fixed chemical composition: Minerals are unique chemical compounds.

For example, the mineral halite (rock salt, below)) consists only of the elements sodium (Na) and Chlorine (Cl). In halite, these elements are always combined in a 1:1 ratio (fixed chemical composition) and are always arranged in a repeating framework (crystalline solid).

There are 92 different elements that occur in nature. Fortunately for geologists, only 8 elements are common in the Earth's crust.

Silicon (Si) and oxygen (O) are by far the most common elements in the Earth's crust, and readily combine with each other. Because of this, silicate minerals are the most abundant minerals on Earth. In these minerals, Si ions are attached to four O ions, giving the complex ions (SiO₄)^-4. These groups take the form of a tetrahedron where the four oxygens form the corners of the group, with Si at in the center.

The many different silicate minerals that make up most of the Earth's crust are formed by linking SiO₄ tetrahedra in different ways, and by incorporating other elements.

Each mineral's crystalline structure and chemical composition is unique. Because of this, each mineral has a unique set of physical properties. These physical properties are used to identify minerals. Important physical properties include;

1. Color

2. Luster

3. Cleavage and fracture

4. Hardness

5. Density

Rocks: Aggregates of one or minerals.

Three categories of rocks: Igneous rocks, Sedimentary rocks, Metamorphic rocks.

Igneous rocks: Form through the cooling and crystallization of molten rock.

1. Volcanic (extrusive) rocks: Crystallize from lava erupted onto the Earth's surface. Volcanic rocks cool rapidly, so mineral crystals have little time to form. These rocks tent to be fine-grained or glasses.

2. Plutonic (intrusive) rocks: Crystallize form magma at depth. These rocks do not reach the Earth's surface. Plutonic rocks cool slowly, so crystals have ample time to grow. Plutonic rocks tend to be coarse-grained.

Sedimentary rock: Rocks formed from the fragments of older rocks.

Rocks exposed to the atmosphere experience physical and mechanical weathering, and are broken into small fragments (gravel, sand, silt, clay) or are partially dissolved in water.

Weathered fragments and dissolved material are transported to other locations and are deposited as sediment. These loose sediments are changed to rocks by different processes collectively called lithification. For example, sand and gravel can be cemented together to form sandstone and conglomerate.

Metamorphic rocks: Rocks that change from one form to another as a response to changing conditions of temperature and pressure. Different conditions cause some minerals to breakdown, and new minerals to form.

Different types of metamorphic rocks will form under different conditions of heat and pressure. The more deeply a rock id buried, the more heat and pressure it is subjected to. With increasing depth, shale (a sedimentary rock) will transform into slate, phyllite, schist, and gneiss.