Minerals, Rocks, and the Rock Cycle: Key Concepts and Processes

Mineral

A naturally occurring, inorganic solid with a definite chemical composition and a crystalline structure.

Five key characteristics of a mineral

Naturally occurring, inorganic, solid, definite chemical composition, and crystalline structure.

Difference between minerals and rocks

A mineral has a specific composition and structure, while a rock can be made of one or more minerals.

Three main rock types

Igneous, sedimentary, and metamorphic.

Formation of igneous rocks

From the cooling and solidification of molten rock (magma or lava).

Formation of sedimentary rocks

From compaction and cementation of sediments or precipitation of minerals.

Formation of metamorphic rocks

From alteration of existing rocks under heat, pressure, or chemical processes.

Rock cycle

A series of processes that transform rocks from one type into another over time.

Processes turning igneous rocks into sedimentary rocks

Weathering, erosion, deposition, compaction, and cementation.

Processes forming metamorphic rocks in the rock cycle

Heat, pressure, and chemical changes.

Igneous rocks at divergent boundaries

Basalt and gabbro (mafic rocks).

Igneous rocks at convergent boundaries

Andesite, diorite, rhyolite, and granite (intermediate and felsic).

Igneous rocks at hotspots

Typically basaltic rocks, sometimes rhyolite at continental hotspots.

Volcanic (extrusive) igneous rocks

Rocks formed from lava that cools quickly at the surface.

Plutonic (intrusive) igneous rocks

Rocks formed from magma that cools slowly underground.

Texture differences in volcanic vs plutonic rocks

Volcanic rocks have fine-grained or glassy textures, while plutonic rocks are coarse-grained.

Physical (mechanical) weathering

The breakdown of rocks into smaller pieces without changing composition.

Chemical weathering

The breakdown of rocks by chemical reactions, altering composition.

Major mechanisms of erosion

Water, wind, ice (glaciers), and gravity.

Clastic sedimentary rocks

Rocks made from fragments of other rocks compacted and cemented together.

Biochemical sedimentary rocks

Rocks formed from the remains of living organisms (e.g., fossiliferous limestone).

Chemical sedimentary rocks

Rocks formed when minerals precipitate from solution (e.g., rock salt).

Sedimentary rocks revealing Earth's history

They preserve fossils and stratification, showing past environments.

Factors causing metamorphism

Heat, pressure, and chemically active fluids.

Contact metamorphism

Localized metamorphism from heat of nearby magma.

Regional metamorphism

Large-scale changes due to high pressure and temperature, often from tectonic compression.

Texture differences between contact and regional metamorphism

Contact produces non-foliated rocks, regional produces foliated rocks.

Importance of sedimentary rocks in interpreting past environments

They record depositional settings such as rivers, oceans, or deserts.

Fossils in sedimentary rocks

They provide evidence of past life and environmental conditions.

Chemical signatures in sedimentary rocks

They reveal changes in climate, ocean chemistry, and atmosphere over time.