Introducing Earth Classifying RocksClassifying Rocks

Classifying Rocks Minerals are solid, naturally occurring substances. Many of the particles that make up rocks are minerals. Rocks are made up of mixtures of minerals and other substances. Minerals are solid, naturally occurring substances. Many of the particles that make up rocks are minerals. Rocks are made up of mixtures of minerals and other substances. A single rock can contain a single mineral or several minerals depending on the type of rock. A single rock can contain a single mineral or several minerals depending on the type of rock. When geologists study rock samples they look at three components: the rock mineral composition, color & texture When geologists study rock samples they look at three components: the rock mineral composition, color & texture

Mineral Composition & Color Approximately 20 rock-forming minerals can be found in the Earth’s crust. Approximately 20 rock-forming minerals can be found in the Earth’s crust. A rock’s color can give clues as to what minerals it contains. A rock’s color can give clues as to what minerals it contains. The granite rock as shown above is made up of 4 different types of rock-forming minerals: Feldspar, Hornblende, Quartz & Mica

Texture Most rocks are made up of particles of minerals or other rocks, which geologists call grains. Grains give the rocks its texture. Texture is the look and feel of a rock’s surface. To describe the texture of a rock, geologists use terms that are based on shape, size, and pattern of the grains

Texture

Classifying Rocks Geologists use color, texture and mineral composition to classify rock according to its origin Geologists use color, texture and mineral composition to classify rock according to its origin A rock’s origin is the way that the rock was formed A rock’s origin is the way that the rock was formed There are there are three categories in which geologist classify rocks: There are there are three categories in which geologist classify rocks:  Igneous Rock  Sedimentary Rock  Metamorphic Rock

Classifying Rocks Metamorphic Rock Forms when a rock is changed by heat or pressure, or by chemical reactions. Most metamorphic rock forms deep underground Igneous Rock Forms from the cooling of molten material called magma or lava. Magma hardens underground to form rock. Lava erupts, cools, and hardens to form rock on Earth’s Surface Sedimentary Rock Forms when small particles of rocks or the remains of plants and animals are pressed and cemented together. Sedimentary forms in layers that are below the surface.