Mineralogy Basics: Rock-Forming Minerals

Study Notes

Minerals are crystalline, inorganic substances with unique physical properties.
Hardness measures resistance to abrasion.
Luster describes the quality and intensity of reflected light from a mineral.
Color can be a unique identifier for some minerals, but variance is common.
Cleavage refers to the tendency of a mineral to break along parallel, smooth planes.
Fracture refers to the tendency of a mineral to break along irregular, non-planar surfaces.

Quartz is hard, glassy-looking, and can be transparent or translucent.
Feldspar is dull, opaque, and porcelain-like, with colors ranging from red to green.
Mica is easily separated into thin sheets and can be white (muscovite) or black (biotite).
Pyroxene is dark green to black and often forms short, stubby crystals.
Amphibole crystals are longer, thinner, and shinier than pyroxene.
Olivine is yellow-green, translucent, and glassy-looking; not commonly found as crystals.

Igneous rocks form from the solidification of molten rock.
Extrusive igneous rocks solidify at the surface from lava.
Intrusive igneous rocks solidify below the surface from magma.
Sedimentary rocks are formed from weathering and erosion of existing rocks.
Clastic sedimentary rocks are composed of fragments of other rocks.
Chemical and organic sedimentary rocks form by precipitation from solutions or organic processes.
Metamorphic rocks are formed from existing rocks transformed by heat and pressure.

Rocks are constantly being transformed through processes like weathering, erosion, deposition, heat, and pressure.
This cycle creates a continuous loop of creation and transformation of rocks.

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