Different Types of Rocks

6th Grade

How do Rocks form?

• Igneous Rocks: forms from the cooling of magma or lava

• Sedimentary Rocks: forms when particles of other rocks or the remains of plants and animals are pressed and cemented together

• Metamorphic Rocks: forms when an existing rock is changed by heat, pressure or chemical reactions

How can one classify rocks?

• By its texture: the look and feel of the rock’s surface

• Grains: particles of minerals or other rocks – Give a rock its texture

To describe a rock’s texture, geologists use terms based on the size, shape, and pattern of the grains

Grain Size

– 1) Fine Grain: grains are so small that they can only be seen with a microscope

Grain Size

- 2) Coarse grain: grains in a rock are large and easy to see

Grain Shape

1) Rounded Grain: (Conglomerate)

2) Jagged Grain: (Breccia)

Grain Pattern

• Non-banded: – No patterns or bands

noticeable

• Banded: (foliated)– Grains lie in bandsof different colors

Igneous Rocks: “Igneous” comes from Latin word “ignis” which means “Fire”

• 1) Extrusive rock = igneous rock formed from lava that erupted onto Earth’s surface

• 2) Intrusive rock = igneous rock that is formed when magma is hardened beneath the Earth’s surface

Types of Igneous Rocks

• Extrusive Rocks have a fine-grained or glassy texture

• Intrusive Rocks have larger crystals in them because they cool more slowly

Sedimentary Rocks

• What is sediment? – Small, solid pieces of material that come from

rocks or living things – ex. Sand grains, mud, pebbles AND shells, bones, leaves, stems, remains of living things

Sedimentary Rocks: formed from erosion, deposition, compaction, cementation

• Erosion: running water, wind, or ice loosen and carry away fragments of rock.

• Deposition: the process by which sediment settles out of the water or wind carrying it

• Compaction: the process that presses sediments together

• Cementation: the process in which dissolved minerals crystallize and glue particles of sediment together

Types of Sedimentary Rocks

• Clastic Rock: a sedimentary rock formed when rock fragments are squeezed together

• Organic Rock: a sedimentary rock formed when the remains of plants and animals are deposited in thick layers

Metamorphic Rocks: “meta” = change and “morphosis” = form

• Rocks that are changed by heat and pressure deep beneath the Earth’s surface

• Metamorphic rocks can form out of igneous, sedimentary, or other metamorphic rock

• Collisions between Earth’s plates can push the rock down toward the heat of the mantle

Metamorphic Rocks

• Foliated: have their grains arranged in parallel layers or bands

• Nonfoliated: mineral grains in these rocks are arranged randomly

• Granite turns into Gneiss

• Shale turns into Slate

• Limestone turns into Marble