Rocks and The Rock Cycle In order to begin a discussion to understand what a rock is, we need to recall what a mineral is. What are the 5 properties that determine if something is a mineral? -

Rocks and The Rock Cycle In order to begin a discussion to understand what a rock is, we need to recall what a mineral is. What are the 5 properties that determine if something is a mineral? Must occur naturally. Must be inorganic ( not from living organisms) Must be solid. Must have a crystal structure Must have a definite chemical composition ( chemical formula)

Rocks and The Rock Cycle A rock is a solid mixture of one or more minerals. The picture below shows a piece of granite, which is a go-to example of a rock

Difference between a mineral and a rock? Minerals tend to have a characteristic crystal structure based on chemical composition, Rocks have many minerals in them, so they do not have a definite structure. Granite (rock) is made of feldspar, quartz, amphibole, mica, pyroxene, etc (all minerals).

Rocks and the Rock Cycle The Three Rock Types Include: Igneous Rocks (i.e. Fire Rocks – from molten material) Sedimentary Rocks (i.e. Layered Rocks – from deposition) Metamorphic Rocks (i.e. Changed Rocks) All three rock types are interrelated through the rock cycle. The three rock types are classified by their nature of origin (i.e. formation). Reference: Tarbuck and Lutgens Pages 15 - 17

Igneous Rocks Rocks that have solidified from a molten state. If the molten material is located below Earth’s surface, then it is called magma. Magma is higher in gases than lava. If the molten material is located on Earth’s surface, then it is called lava. Lava is lower in gases than magma.

Igneous Rocks There are two classifications of igneous rock, which include: 1) Plutonic (intrusive) – forms from magma. Forms inside the earths crust 2) Volcanic (extrusive) – forms from lava. On Forms on earth’s surface

Igneous Rocks Examples include: Granite (Intrusive) and Rhyolite (Extrusive) Diorite (Intrusive) and Andesite (Extrusive) Gabbro (Intrusive) and Basalt (Extrusive) Peridotite (Intrusive) and Komatiite (Extrusive) Note that both rocks in each pair exampled above has the same composition; however, one formed from a lava and one formed from a magma.

What can you tell about these rocks that have the same composition but are either intrusive or extrusive? Extrusive Intrusive Extrusive Intrusive Extrusive Extrusive Intrusive Intrusive

Extrusive Vs. Intrusive Igneous Rocks Extrusive are on the surface - cool quickly, no time to form, so have small grains Intrusive are in the earth - cool slowly, have time to form so have larger grains

Sedimentary Rocks Rocks formed when the weathered products (i.e. sediment) of pre-existing rocks have been transported, deposited, compacted, and cemented into solid rock. These rocks usually show layering/strata/beds. Usually formed in water environments. For example, sediment being deposited by streams and rivers. Most of Earth’s crust (95%) is igneous rocks; however, the surface of the crust is largely covered by sedimentary rocks. The Three classifications of Sedimentary Rocks include: Clastic (i.e. Detrital) Chemical Organic (Biogenic)

Sedimentary Rocks Examples include: Shale, Siltstone, Sandstone, Breccia, Conglomerate, Limestone, Dolomite, Chalk, Coquina, Coal. Note that clastic (i.e. detrital) sedimentary rocks are classified by grain size.

Clastic (i.e. Detrital) sedimentary Rocks Formed by deposition of rock and mineral fragments

Chemical sedimentary Rocks formed from minerals that were carried in solution (dissolved in water) and are deposited as precipitates.

Organic (Biogenic) Sedimentary Rocks formed from the remains of dead animals. Chaulk Limestone

Metamorphic Rocks Rocks formed below Earth’s surface when pre-existing rocks (i.e. igneous, sedimentary, and even metamorphic) are altered 3 Agents of Metamorphisism: heat, pressure, and chemically active fluids (e.g. water). NOTE: MELTING IS NOT INVOLVED IN THE PROCESS OF METAMORPHISM.

Metamorphic Rocks Metamorphism changes rocks in size, shape, texture, and mineral composition. Metamorphism varies in degree from: High Grade. E.g. Granite changes to Gneiss Low Grade. E.g. Shale changes to Slate

Metamorphic Rocks Examples of metamorphic rocks include: Quartzite, Marble, Slate, Slate, Phyllite, Schist, and Gneiss. Note that there are two types of metamorphism, which include: Contact and Regional.

Pre-notes on the Rock Cycle A) All three types of rocks could be weathered and eroded compacted into sedimentary layers. B) All three types of rocks could be metamorphosed if subjected to appropriate conditions of metamorphism (for example: heat, pressure, chemically-active fluids). C) All three types of rocks could be melted if the temperatures become high enough. D) Once melting to a molten has occurred, igneous activity has begun. E) The process of melting is not involved in metamorphism. If it melts, it becomes liquid rock, which will then cool to form Igneous Rock.

http://www.learner.org/interactives/rockcycle/diagram.html http://www.geolsoc.org.uk/ks3/gsl/education/resources/rockcycle/page3892.html

Rock Cycle Magma/Lava Metamorphic Igneous (Volcanic) (Plutonic) Melting Cooling and Crystallization (i.e. solidification) Metamorphic Igneous (Volcanic) (Plutonic) Heat, Pressure, and Hot Chemical Fluids Heat, Pressure, and Hot Chemical Fluids Melting Sedimentary (Clastic) (Chemical) (Organic) Weathering And Erosion Weathering And Erosion Weathering And Erosion Compaction And Cementing Sediment Examples include: sand, silt, and clay (mud)

Sample Problem In the diagram below, rock types/materials are indicated by numbers and processes are indicated by letters. Indicate the rock types/materials and processes for the rock cycle diagram by completing the table below. Answer: A 1. Magma E 2. 5. B D Weathering & Erosion C 3. 4. Rock Type / Materials Processes 1. Magma A Cool & Crystallize 2. Igneous B Weathering and Erosion 3. Sediments C Compacting & Cementing 4. Sedimentary D Heat & Pressure 5. Metamorphic E Melting