Minerals - The Earth’s Building Blocks

A mineral is a naturally occurring, inorganic material with a definite crystal structure and chemical composition

No two minerals have both the same crystal structure and composition

Physical properties are the easiest (but least exact) way to identify them

Mineral Crystals

Each mineral’s crystal structure is due to the regular repeating pattern of atoms which make up the chemical composition of the mineral

Example: Halite (NaCl)

Rocks

A rock is an aggregate or mixture of crystals from one or more minerals

Rock Types

Igneous Rocks - formed from the cooling of magma

Sedimentary Rocks - formed from the lithification of sediment

Metamorphic Rocks - formed by the alteration of other rocks through the addition of heat and /or pressure

Igneous Rocks

Formed from molten magma (= lava at the Earth’s surface)

Intrusive or plutonic igneous rocks cool slowly far below Earth’s surface. Mineral crystals have time to grow big.

Extrusive or volcanic igneous rocks cool quickly at or near the Earth’s surface. Mineral crystals quench quickly and are small (microscopic) in size.

Sedimentary Rocks

Formed by lithification of sediment at the Earth’s surface

Sediment may be either:

Clastic: detrital (rock fragments)

Non-clastic: chemically deposited

Characteristics of sedimentary rocks

Usually layered

Often contain fossils

Metamorphic Rocks

Formed by changing any rock type by the addition of heat and/or pressure

Metamorphic Rock Classification

Non-foliated (recrystallized)

Limestone – Marble

Sandstone - Quartzite

Foliated (layered)

Fine-grained- Slate - Schist

Coarse - Grained rock – Gneiss

Rock Cycle

No single rock has remained unchanged since the amalgamation of the Earth ~ 4.5 Ga

Plate tectonics shows that oceanic crust is constantly being generated and destroyed

Similarly, continental crust is constantly being altered by tectonic forces, weathering, and erosion

These result in a rock cycle where all rocks are constantly being altered and changed into other rocks

Weathering

Weathering is the physical or chemical breakdown of rocks at the Earth’s surface (critical element of rock cycle)

Physical Weathering

Creates rock fragments with no change in composition

Wind, water, relief, temperature, and plant cover are key factors

Chemical Weathering

chemical alteration of minerals to form new minerals

Erosion

Erosion is the process of removing unconsolidated Earth material and transporting it to other depositional sites (mainly the oceans)

Wind, water, ice, and gravity are transport agents

Erosion rates depend on climate, relief, and degree of weathering

Products of Weathering and Erosion

Solid material

Rock fragments (gravel, sand, silt, clay)

New minerals from chemical weathering

Chemical precipitates

Biological materials (shell, bones, organics)

Dissolved material

Gases from atmosphere and chemical reactions

Dissolved solids - inorganic and organic

Water as a Geologic Agent

Water Abrasion (weathering)

Water and particles carried in water actively weather (physically) earth materials

Chemical ions in water also chemically weather earth materials

Water Transport (erosion)

Deposition by Water (sedimentation)

Clastic sedimentary rocks

Chemical sedimentary rocks

Wind as a Geologic Agent

Wind Abrasion (weathering)

Causes deflation of unconsolidated sediment

Causes physical erosion of resistant material

Wind may carry sediment 1000s of km (erosion)

Sediment Deposition

Loess sediments

Dunes

Continental Sites of Deposition

All solid materials are moved toward local depressions, like lakes and valleys, where they are deposited

Enroute, the particles are sorted by size - coarsest materials stay closest to source

Eventually most particles reach the oceans - but their movement may involve several steps by different processes over long periods of time