1. Rocks

2. What are Rocks?
Rocks are a combination of minerals that are bonded together in some way.
All rocks are made of minerals
Monomineralic- contain one mineral Polymineralic- contain more than one mineral
Rocks are classified into three groups by how they are formed

3. 3 types of Rocks
Metamorphic Rocks: are formed when old rocks change by heat and pressure.
Sedimentary Rocks: Form from sediments (pieces of other rocks) that are cemented together.
Igneous Rocks: Form from molten rock that cools and hardens.
Rocks are classified by how they form

4. Igneous means “born of fire”
The Rock Cycle
Igneous
Igneous means “born of fire”

5. Igneous means “born of fire”
The Rock Cycle
Igneous : Form from the cooling and hardening of Magma or lava.
Igneous means “born of fire”

6. Igneous Rocks
Form from liquid (molten) rock called Magma or Lava that cools and hardens (solidifies)
All igneous rocks are identified on the basis of composition and texture
The rate at which rocks cool from the liquid magma determines their texture.
Faster it cools, the smaller the crystals
Slower it cools, the larger the crystals

7. Classification of igneous rocks- 2 types
Intrusive
Form from magma
Cooled and solidified slowly deep underground
Extrusive
Form from lava
Cooled quickly at or near the surface of the earth.

8. Igneous rocks are also formed causing the magma to rise
when volcanoes erupt,
causing the magma to rise
above the earth's surface.

10. Igneous Rocks
Can be:
Felsic: light colored rocks that are rich in elements such as aluminum, silicon. Lower density
Mafic: dark colored rocks that are rich in iron and Mg. Higher density
Coarse-grained texture: takes longer to cool, larger visible mineral crystals
Fine-grained texture: cools quickly with small mineral crystals
Glassy Texture: cools the quickest, no mineral crystals form
Vesicular texture: Gas pockets (holes)
(note) Texture refers to the size/appearance of the minerals

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

12. Minerals in Igneous rocks
Plagioclase felspar- most common mineral found in igneous rocks
Quartz- looks dark and glassy
Potassium feldspar
Muscovite- not that common
Biotite- occurs in small amounts
Pyroxene
Olivine

13. Igneous Rocks Is this rock Felsic or Mafic?
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?

14. Glassy Texture
                                                                    Glassy textured igneous rocks are non-crystalline meaning the rock contains no mineral grains. Glass results from cooling that is so fast that minerals do not have a chance to crystallize. This may happen when magma or lava comes into quick contact with much cooler materials near the Earth's surface. Pure volcanic glass is known as obsidian (see photo).

15. Vesicular Texture
                                                                               This term refers to vesicles (holes, pores, or cavities) within the igneous rock. Vesicles are the result of gas expansion (bubbles), which often occurs during volcanic eruptions. Pumice and scoria are common types of vesicular rocks. The image to the left shows a basalt with vesicles, hence the name "vesicular basalt".

16. Fragmental Texture
                                                                         The last textural term
reserved for pyroclastic rocks, those blown out into the atmosphere during violent volcanic eruptions. These rocks are collectively termed fragmental. If you examine a fragmental volcanic rock closely you can see why. You will note that it is comprised of numerous grains or fragments that have been welded together by the heat of volcanic eruption. If you run your fingers over the rock it will often feel grainy like sandpaper or a sedimentary rock. You might also spot shards of glass embedded in the rock.

17. Types of igneous rocks Granite- most abundant igneous rock
Can be made up of feldspar, quartz, mica, and hornblende

18. Obsidian
Obsidian rocks are igneous rocks that form when lava cools quickly above ground.
Obsidian is actually glass and not a mixture of minerals. The edges of this rock are very sharp.

19. Pumice
Pumice rocks are igneous rocks which were formed when lava cooled quickly above ground.
This rock is so light, that many pumice rocks will actually float in water.
Pumice is actually a kind of glass and not a mixture of minerals.

20. Extrusive
Insrusive