Understanding Rock and Mineral Formation and Change

Igneous Rocks Igneous means “born of fire” Igneous rocks are created by cooling of molten magma

What is a rock? A rock is a solid mixture of minerals. Ex: Quartz, feldspar, mica and hornblende combine to form granite

Intrusive Igneous Rocks Form or crystallize within the earth Cool slowly and therefore form large crystals Considered “coarse grained” Examples are granite and gabbro

Granite

Gabbro

Extrusive Igneous Rocks Form above the surface Lava cools quickly when exposed to air Forms small crystal Fine grained texture Frothy texture Glassy texture Examples: Basalt and Obsidian

Relationships between: Magma depth Cooling rate Crystal size

Textures Frothy Texture Fine grained texture

Basalt

Basalt (continued) The most common form of igneous rock Makes up most of the ocean floor Smooth and velvety black Very hard Tiny crystals

Pumice Floats on water Trapped bubbles of carbon dioxide form holes

Obsidian Glassy texture

Sedimentary Rocks Form on surface of the earth Often layered (bedded) May contain fossils or evidence of living organisms

Weathering In order to understand how sedimentary rocks form, one must understand how existing rocks are broken down by physical and chemical weathering Weathering prepares rocks for erosion and transforms rocks into the raw materials that will become sedimentary rocks Two types: Chemical and Physical

Weathering (continued) Weathering refers to the group of destructive processes that change the character of the rock at or near the earth’s surface Mechanical weathering breaks rock into smaller pieces: an example is water freezing and expanding in cracks causing rock to break apart Exposure to carbon dioxide and water can cause Chemical weathering as well

Erosion and Weathering Once weathering has occurred, erosion – the picking up and physical removal of rock particles can happen quickly Finally, weathered and eroded material can be transported by rivers, streams and glaciers What are some methods of erosion?

Water Erosion

Wind Erosion

Examples of Weathering

Examples of Erosion

How sedimentary rocks form: Compaction, cementation and crystallization

Types of Sedimentary Rocks Clastic: compaction and cementation of sediments or rock particles (shale) Chemical: precipitation of minerals from solution (limestone) Organic: consolidation of the remains of plants and animals (coal)

How can you spot a Sedimentary Rock? Sedimentary rock will often have bands or layers across It will often contain fossils which are fragments of animals or plants preserved within the rock The rock will tend to scrape easily and crumble easily

Examples of Sedimentary Rock Sandstone

Limestone Fossiliferous Limestone

Coquina

Shale

Metamorphic Rocks Formed from either existing igneous or sedimentary rocks Formed under tremendous heat and pressure Do NOT melt Formed deep underground Associated with mountain building Often foliated or flaky

Classifying Metamorphic Rocks Foliated: seems to have layers or thin lines – appears almost flakey Nonfoliated: Uniform in composition – no lines or obvious layers Foliated Nonfoliated

Quartzite

Marble

Hornblende

Schist