Minerals and Rocks Overview

Overview

This lecture explains what minerals and rocks are, how to identify minerals, the classification of rock types, and the basics of the rock cycle.

A mineral is an inorganic, naturally occurring solid with a definite chemical composition and atomic structure.
Inorganic means not living, never was living, and not composed of organic matter.
Minerals must occur naturally and be solid under Earth's surface conditions.
Key identification properties: color, hardness (Mohs scale, 1-10), luster (metallic or non-metallic), streak (color in powdered form), cleavage (predictable break), fracture (random break), magnetism, taste, odor, reaction to acid, and fluorescence.
Example minerals: potassium feldspar (orthoclase), sulfur, muscovite mica, galena, calcite, olivine, quartz.
Example: Galena—metallic, soft, cleavage, dense, ore of lead; Olivine—hard, fracture, non-metallic, used in jewelry.

Rocks are made from minerals and classified based on formation: igneous, sedimentary, metamorphic.

Formed from cooling and solidification of magma or lava.
Extrusive (volcanic): lava cools quickly at surface, small or no visible crystals (e.g. basalt, rhyolite, obsidian, pumice, vesicular texture).
Intrusive (plutonic): magma cools slowly underground, large crystals visible (e.g. granite, pegmatite).
Light-colored rocks are felsic (rich in silicon and aluminum); dark-colored are mafic (rich in iron and magnesium).
Crystal size is determined by cooling speed: slower cooling = larger crystals.

Formed from compaction and cementation of sediments (pieces of other rocks).
Clastic rocks: made of cemented sediments, classified by sediment size (e.g. conglomerate, breccia, sandstone, siltstone, shale).
Crystalline rocks: form by evaporation or precipitation of minerals from water (e.g. rock salt).
Bioclastic rocks: formed from compacted organic matter (e.g. limestone from shells, coal from plants).
Processes: weathering, erosion, deposition, burial, compaction, cementation.

Formed by intense heat and/or pressure changing existing rocks.
Foliated rocks: show mineral alignment or banding due to pressure (e.g. slate, schist, gneiss—only gneiss has banding).
Nonfoliated rocks: formed mainly by heat or pressure without mineral alignment (e.g. anthracite coal, quartzite, marble).
Metamorphism can be regional (pressure) or contact (heat from nearby magma).

Rocks continuously change types through weathering, melting, pressure, and heat.
Any rock type can become another through these processes.

Mineral — A naturally occurring, inorganic solid with definite chemical composition and structure.
Cleavage — Tendency of a mineral to break along flat planes.
Fracture — Irregular, random breakage of a mineral.
Luster — How a mineral reflects light (metallic or non-metallic).
Streak — Color of a mineral in powdered form.
Igneous Rock — Rock formed from cooled magma or lava.
Sedimentary Rock — Rock formed from compacted and cemented sediments.
Metamorphic Rock — Rock altered by heat and/or pressure.
Foliation — Alignment or banding of minerals in metamorphic rocks.

Review mineral and rock identification charts in the Earth Science Reference Tables.
Practice distinguishing rock types and mineral properties for identification.