Today’s Agenda 1. Post assessment 2. Test – Take out a sheet of paper (25 question). Add question 25. Q 25. What does it mean if a mineral is inorganic ? 3. Relative Dating worksheet 4. Lab. – Identify Igneous Rocks

Rocks and its Types

What are Rocks? A rock is a naturally occurring solid mixture of one or more minerals, or organic matter Rocks are classified by how they are formed, their composition, and texture Rocks change over time through the rock cycle

Igneous Rocks Igneous rock begins as magma. Magma can form: When rock is heated When pressure is released When rock changes composition Magma is a mixture of many minerals http://www.fi.edu/fellows/payton/rocks/create/igneous.htm

Igneous Rocks Coarse-grained: takes longer to cool, giving mineral crystals more time to grow Fine-grained: cools quickly with little to no crystals Big crystals cool slow Small crystals cool fast

Igneous Rocks Coarse-Grained Fine-Grained Felsic Granite Rhyolite Mafic Gabbro Basalt

Igneous Rocks Intrusive Igneous Rocks: magma pushes into surrounding rock below the Earth’s surface Extrusive Rocks: forms when magma erupts onto the Earth’s surface (lava), cools quickly with very small or no crystals formed http://www.windows.ucar.edu/tour/link=/earth/geology/ig_intrusive.html&edu=high&fr=t

Mafic, fine grained, extrusive Obsidian What is Obsidian? Obsidian is a dark-colored volcanic glass that forms from the very rapid cooling of molten rock material. It cools so rapidly that crystals do not form. Igneous Rocks Obsidian is a dark-colored volcanic glass that forms from the very rapid cooling of molten rock material. It cools so rapidly that crystals do not form. Is this rock Felsic or Mafic? Is it fine-grained or coarse-grained? Is this rock Intrusive or Extrusive? Mafic, fine grained, extrusive

Metamorphic Rock Changes with heat and pressure, but remains solid Means to change shape Changes with heat and pressure, but remains solid Usually takes place deep in the Earth http://www.fi.edu/fellows/payton/rocks/create/metamorph.htm

Metamorphic Rock Foliated - contain aligned grains of flat minerals (lines) Gneiss is foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains. It typically contains abundant quartz or feldspar minerals.

Metamorphic Rock Non-Foliated – mineral grains are not arranged in plains or bands Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone. It is composed primarily of calcium carbonate.

Metamorphic Rock Determine if the following rock samples are foliated or non-foliated: Quartzite Amphibolite Phyllite Foliated

Sedimentary Rocks Sedimentary rock is formed by erosion Sediments are moved from one place to another Sediments are deposited in layers, with the older ones on the bottom The layers become compacted and cemented together http://www.fi.edu/fellows/payton/rocks/create/sediment.htm

Sedimentary Rock Sedimentary Rocks are formed at or near the Earth’s surface No heat and pressure involved Fossils found in these rocks Strata – layers of rock Stratification – the process in which sedimentary rocks are arranged in layers

Sedimentary Rock Clastic – made of fragments of rock cemented together with calcite or quartz Breccia is a term most often used for clastic sedimentary rocks that are composed of large angular fragments (over two millimeters in diameter). The spaces between the large angular fragments can be filled with a matrix of smaller particles or a mineral cement that binds the rock together.

Sedimentary Rock Chemical sedimentary – minerals crystallize out of solution (water) to become rock Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO3) in the form of the mineral calcite. It most commonly forms in clear, warm, shallow marine waters. It is usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal and fecal debris.

Sedimentary Rock Organic sedimentary – remains of plants and animals Coal is an organic sedimentary rock that forms from the accumulation and preservation of plant materials, usually in a swamp environment.  Coal is a combustible rock and along with oil and natural gas it is one of the three most important fossil fuels. 

Rock Cycle The continuous changing of rocks from one kind to another over long periods of time is called the rock cycle. The rock cycle has no definite sequence. It can follow many different pathways.

Rock Cycle Igneous: Melting to Magma/Volcanic Activity Sedimentary: Erosion – Weathering-Deposition - Cementation – Compaction Metamorphic: Heat and Pressure

Fossils Fossils are found in Sedimentary rocks They help provide information of life forms that lived thousands of years ago.

Types of Fossils Petrified – Minerals have filled in where an organisms once was Molds – A hollow area that an organism has left. Cast – A copy of the shape of the organism (opposite of a mold) Carbon Film – a thin coating of carbon that is left behind when gases have been release by the decaying fossil (like a leaf print on a rock) Trace – An imprint that an organism left behind (like a footprint)

Petrified Fossils Fossils in which minerals replace all or part of an organism. How does this happen? Water rich in dissolved minerals seeped into spaces, evaporated, leaving the hardened minerals behind. Example – petrified wood

Molds and casts Most common type of fossil. Both copy the shape of the organism. A mold is a hollow area of sediment in the shape of the organism. A cast is a copy of the shape of an organism.

Carbon Films Carbon film is an extremely thin coating of carbon How does this happen? All organisms are made of carbon. When they are buried, the materials that make up the organism evaporates. These gases escape leaving carbon behind.

Trace Fossils Trace fossils provide evidence of the activities of ancient organisms. Examples A footprint provide clues about the size and behavior, the speed, how many legs it walked on, lived alone or with others. A trail or burrow can give clues about the size and shape of the organism, where it lived, and how it obtained food.

How old is it? Relative Age – It’s age when compared to others ( I am older than you) Absolute age – It’s actual or real age We use radioactive dating to find this Unconformity – a gap in the the geological record (like from erosion)

Geological Laws https://www.youtube.com/watch?v=Vhwd56BNcL0 https://www.youtube.com/watch?v=EadTLGMu3LI

Law of Superposition In horizontal sedimentary rock layers the oldest layer is at the bottom. Each higher layer is younger than the layers below it. https://www.youtube.com/watch?v=YgE-dSx-fPc

The Grand Canyon

Law of Crosscutting Relationships Sometimes magma pushes, or intrudes, into cracks in existing rocks. When the melted rock cools and solidifies, the resulting feature is called an igneous intrusion. An igneous intrusion is always younger than the rock it cuts across. This image shows metamorphic rock in Death Valley, California, cut by a darker igneous intrusion.