1. 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

2. Rocks and its Types

3. 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

4. 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

5. 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

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

7. 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

8. 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

9. 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

10. 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.

11. 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.

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

13. 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

14. 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

15. 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.

16. 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.

17. 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. 

18. 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.

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

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

22. 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)

23. 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

24. 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.

25. 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.

26. 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.

27. 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)

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

29. 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.

30. The Grand Canyon

31. 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.