Rocks Classifying Rocks When studying a rock sample

Rocks Classifying Rocks

�When studying a rock sample, geoliogists observe the rock’s mineral composition, color, and texture. Rock Study

�Rocks are made of mixtures of minerals and other materials. � 20 minerals make up most of the Earth’s surface. �We call these minerals rock-forming minerals. Mineral Composition

�A rock’s color provides clues to the rock’s mineral composition. �Usually lighter the color rock, the more silica present. The darker, less. �Geologists observe the shape and color of crystals in a rock to identify the minerals that the rock contains. �Acid is put on rocks to see the presence of carbonates in the rock. Mineral Color

�Most rocks are made up of particles of minerals called grains. �The grains affect the texture of the rock. �The size, shape, and pattern of the grains determine how smooth or rough the rock becomes. Texture

�Large grained rocks are referred to as coarse-grained. �Small grained rocks are referred to as fine grain. �Some rocks have no visible grains. Grain Size

�Rounded �Jagged grain Grain Shape

�Non Banded �Banded Grained Pattern

�You can classify rocks by its origin. A rock’s origin is how the rock formed. �Geologists classify rocks into three major groups: igneous rock, sedimentary rock, and metamorphic rock. How rocks form?

�Igneous Rock �Sedimentary Rock �Metamorphic Rock 3 Types of Rock

�Forms when magma or lava cools and hardens. Igneous Rock

�Forms when pieces of rock are pressed and cemented together. Sedimentary Rock

�Forms from other rocks that are changed by heat and pressure. Metamorphic Rock