Rocks and The Rock Cycle

A rock is a group of minerals bound together.

“The present is the key to the past.” Uniformitarianism “The present is the key to the past.” James Hutton

Uniformitarianism Is based on two ideas: The geologic processes now at work were also active in the past. The present physical features of Earth were formed by these same processes, at work over long periods of time.

Three Types of Rock Igneous Rock is formed by the cooling and hardening of hot molten rock called magma

Three Types of Rock Sedimentary Rock is formed by the hardening and cementing of layers of deposited sediment.

Three Types of Rock Metamorphic Rock is formed when existing rock is changed by heat and pressure into a new kind of rock.

Igneous Rock Molten rock that solidifies inside Earth’s crust forms plutonic (or intrusive) rock. Such rocks are only seen at the surface only after the rock above has been worn away. Granite is an example.

Igneous Rock Plutonic Rock Not in your notes.

Igneous Rock Magma that reaches Earth’s surface is called lava. When lava cools and solidifies, volcanic (or extrusive) rock is formed. Obsidian and pumice are examples.

Pyroclastic Rock = ejected lava Is sorted by size and state at ejection. Volcanic tuff = fine ash and dust. Volcanic breccia = coarse ash and angular pieces.

Types of Magma Felsic Rock (feldspar + silica = felsic) Magma has a high percentage of silica It is low in calcium, magnesium, and iron When it hardens it forms rock that have mainly light-coloured minerals Most plutonic rocks are felsic

Types of Magma Mafic Rock Magma has a lower percentage of silica It is higher in calcium, magnesium, and iron When it hardens it forms rock that have mainly dark-coloured minerals Most volcanic rocks are mafic

Textures of Igneous Rock Texture depends on size, shape, and arrangement of mineral crystals.

Texture Of these, crystal size is the most important. Slower cooling allows crystals time to grow. Also, when the concentration of dissolved gases is high, crystals grow faster. Sometimes molten rock cools so quickly that crystals do not form.

Texture Plutonic rock has a granular or coarse-grained texture. Volcanic rock has a fine-grained texture.

Texture Porphyry Rock: Has two distinct textures and Is thought to be the result of two separate cooling periods. Crystals first begin to form deep below the surface. Then as the magma, laden with crystals, rises, the remainder solidifies.

Families of Igneous Rock Granites Gabbros Diorites

Using Texture to ID. Igneous Rocks Not in your notes.

Different Textures Not in your notes.

Columnar Basalt Not in your notes.

Pillow Basalt Not in your notes.

Not in your notes.

Extrusive Intrusive basalt gabbro andesite diorite rhyolite granite