Minerals, Mohs Scale, and Rock Types: Key Geology Concepts

Mineral

Naturally occurring, inorganic solid formed by natural geological processes, with a definite chemical composition and crystalline structure.

Mohs Hardness Scale

Scale from 1 to 10 measuring hardness or resistance to scratching; 1 is softest, 10 is hardest.

Softest minerals on the Mohs scale

Talc (1) and Gypsum (2).

Hardest mineral on the Mohs scale

Diamond (10).

Cleavage

Breaks along smooth, flat planes.

Fracture

Breaks unevenly with no definite shape.

Streak in minerals

True color of a mineral's powder when rubbed on a surface, sometimes different from surface color.

Luster

Way a mineral reflects light, from shiny (metallic) to dull.

Three main types of rocks

Igneous, Sedimentary, and Metamorphic.

Igneous

Latin word 'ignis,' meaning fire.

Intrusive igneous rocks

Magma cools slowly beneath surface, large crystals.

Extrusive igneous rocks

Lava cools quickly on surface, small or no crystals.

Formation of sedimentary rocks

From sediments being compacted and cemented together.

Metamorphic rocks

Rocks transformed by heat, pressure, and chemical processes.

Metamorphism

Transformation of rocks into metamorphic rocks via contact with magma or regional pressure during mountain formation.

Classifications of metamorphic rocks

Foliated (layered) and non-foliated (not layered).

Formation of foliated metamorphic rocks

Minerals align into layers under directional pressure.

Formation of non-foliated metamorphic rocks

Equal pressure from all sides prevents layer formation.

Rock Cycle

Continuous process of rock formation, breakdown, and transformation.