Geology and Minerals
Rocks, minerals, and the forces that shape the land
Minerals are naturally occurring solids with a defined chemical composition and internal structure. Rocks are aggregates of minerals, and the rock cycle describes how igneous, sedimentary, and metamorphic rocks transform into one another through heat, pressure, erosion, and melting. Plate tectonics drives much of this movement.
Three families of rock
Each rock family forms under different conditions. The diagnostic features below help learners sort specimens by observable evidence rather than appearance alone.
Igneous rocks
Formed when magma or lava cools and solidifies. Crystal size reflects cooling speed: large crystals indicate slow cooling underground, while fine or glassy textures indicate rapid cooling at the surface.
Sedimentary rocks
Formed by the accumulation and cementation of sediments. Look for layering, rounded grains, and fossil fragments. Sandstone, limestone, and shale are common examples.
Metamorphic rocks
Formed when existing rocks change under heat or pressure without melting. Foliation, a banded or aligned texture, often indicates metamorphism, as in slate, schist, and marble.
Classroom diagnostic
Scratching one mineral with another, from the softest to the hardest, reveals which one can leave a mark. The Mohs scale ranks ten reference minerals from talc to diamond, giving learners a simple and repeatable test.
Mohs hardness scale principle