Rocks and the Rock Cycle

Classifying Rocks By: Texture Grain size Shape Patterns Mineral Composition

Texture The look and feel of the rock’s surface. Rough, chalky, smooth or glassy.

Grain Size The size of the actual grain in the rock. They are fined-grained, coarse-grained, or no visible grains.

Grain Shape Is the way a grain looks on a rock.

Grain Pattern The patterns of the grains form are wavy, swirling, or like a stack of planks. Some rocks have no visible grains even under a microscope.

Mineral Composition Will show the mineral composition in the rocks. Minerals are found by a series of tests.

Types of Rocks There are three major types: Igneous – a type of rock formed from the cooling of lava. Sedimentary – a type of rock that forms when sediments are compacted. Metamorphic – forms when existing rocks are changed by heat and pressure.

Igneous Rocks Classified according to their origin, texture, and mineral composition. Extrusive rocks – igneous rocks formed from lava that erupted onto the Earth’s surface. Basalt is the most common extrusive rock.

Igneous Rocks Intrusive Rocks –formed when magma hardened under the Earth. Granite is most abundant intrusive rock in the continental crust. Granite forms the core of many mountain ranges.

Igneous Rocks Basalt is an extrusive rock. Magma that is high in silica usually forms lighted colored rocks such as granite. Many igneous rocks are hard, dense and durable.

Igneous Rock Texture Depends on the size and shape of the mineral crystals. Maybe glassy, coarse-grained, or porphyritic. Intrusive rocks have large grains. Slow cooling magma forms coarse-grained rocks. Extrusive rocks have a fine-grained or glassy texture. Rapid cooling lava forms fine grained rocks.

Igneous Rock Texture Porphyritic rocks have both fine-grains and large crystals scattered throughout. Porphyritic rocks form when intrusive rocks form in 2 stages. Magma begins to cool slowly making large crystals while the other materials around it cool quickly making a fine grained background.

Sedimentary Rocks What is it ? Rocks formed from particles deposited by water and wind. Sediments are small pieces of material that come from rocks or living things. Sediments may include shells, bones, leaves, stems, and other remains of living things.

Erosion and Deposition Wind, water, and ice can carry sediment and deposit it in layers. Erosion breaks up rocks. Deposition is the process by which sediment settles out of the water or wind.

Compaction and Cementation Compaction and cementation over millions of years, thick layers of sediment build up Compaction is the process that presses sediments together. New layers help compact layers underneath. While being compacted minerals slowly dissolve in the water. Minerals seep into spaces between particles of sediment. This is called sedimentation.

Types There are 3 major groups of sedimentary rocks. Clastic forms when rock fragment are squeezed together. Organic forms from remains of plants and animals. Chemical form when minerals are dissolved in a solution crystallize.

Uses Sandstone and limestone have been used as building materials. Limestone is also important when smelting iron ore.

Metamorphic Rock

What is a Metamorphic Rock? Any rock that can be changed into a metamorphic rock by heat and pressure. Can change from igneous, sedimentary, and other metamorphic rocks. The deeper the rock in the Earth the more heat and pressure.

How to classify a Metamorphic Rock? Geologists classify metamorphic rocks by the arrangement of the grains that make up the rocks. Metamorphic rocks have their grains in bands said to be foliated. Metamorphic rocks without bands are called nonfoliated.

Metamorphic Rocks Most of metamorphic rocks are extremely hard. Some examples are slate, gneiss and quartzite which come from shale, granite, and sandstone.

Metamorphic Rocks Metamorphic rocks can be sued for many different things. The Taj Mahal in India is made from the metamorphic rock marble. Chalkboards, flooring, roofing, walkways are created from slate, which comes in different colors.

Metamorphic Rocks Heat and pressure deep beneath the Earth’s surface can change any rock into metamorphic rocks.

Rock Cycle Forces with in the Earth build, destroy, and change rocks. The different paths a rock can take form the Rock Cycle.

Processes within the Rock Cycle Erosion Melting Heat and Pressure

Erosion Melting

Rock Cycle and Plate Tectonics Rock Cycle is driven by Plate Movement Plates press rocks into the mantle, forming magma. Plate movement creates the heat and pressure required for the formation of metamorphic rock.