1. Igneous Rocks!!
Formed from Fire!

2. Rock Types
There are 3 main rock types, and all are interrelated by the ROCK CYCLE!
Igneous
Sedimentary
Metamorphic
Rocks are classified on their origin (where they are from), and how they’re made!

4. Igneous Rocks
They are formed by the cooling and hardening (freezing) of hot, molten rock from within the Earth’s crust
This hot molten rock is a liquid called magma or lava
Magma is molten rock INSIDE Earth and lava is molten rock when it comes up to the surface

5. Igneous Rocks
They are composed of minerals (that’s what rocks are, they’re aggregates of minerals)
The most important ones that make up igneous rocks are:
Plagioclase Feldspar (Ex. Albite)
Potassium Feldspar (ex. Orthoclase) – these are called K-Spar for short…..why?
Quartz
Amphibole (ex. Hornblende)
Olivine
Pyroxene (ex. Augite)
Mica (ex. Muscovite, Biotite, Lepidolite, Chlorite)

7. Igneous Rocks
Crystallization of minerals from magma occurs between degrees C
The minerals with the HIGHEST freezing point crystallize first and thus develop LARGER, well- formed crystals
ENR: Minerals that crystallize at lower temps are forced to grow in the spaces between the earlier formed crystals and are commonly irregular in shape with few well-developed crystals!

8. Igneous Rocks - Classification
Igneous rocks are classified based on where they cool
Extrusive (Volcanic) – these rocks form when hot lava pours out of a volcano and solidifies (NOT inside Earth!)
Cooling is fast (seconds to weeks)
Smaller crystals are formed, some can’t be seen with the naked eye
ESRT!

9. Extrusive (Volcanic)

10. Igneous Rocks
Intrusive (Plutonic)- form from the direct cooling of magma that solidifies beneath the surface
Cooling is slow (up to 1,000,000 years!)
This forms larger crystals, and can be seen with the naked eye

11. Intrusive(Plutonic)

12. Cooling of Igneous rox
Intrusive vs. Extrusive!

13. Igneous Rocks – Types of Magma
All magma is composed of a hot solution of silicates (greater than 1100 degrees C)
Felsic Magma (high in silica) – thick and has a high % of quartz
Low Density
More Aluminum
Light in color
Forms rocks composed of quartz, orthoclase, muscovite, and some amphibole

14. Igneous Rocks
Mafic Magma (low in silica) – more fluid, has less quartz
High Density
Hotter
More Ca, Fe, Mg
Dark in color
Forms rocks composed of hornblende, pyroxene, biotite, and olivine

15. Igneous Rocks - Textures
Textures can range from glassy (obsidian) to coarse (granite)
The crystal sizes depends on the cooling rate!
Slow cooling  large crystals (coarse grained) – these crystals can be seen with the naked eye
Which environment do coarse grained igneous rocks form in? - INTRUSIVE
Coarse grained also called Phaneritic
Fast cooling  small crystals (fine grained) – can not be seen with the naked eye
How about this one? Where does it form? – EXTRUSIVELY
Fine grained is also called APHANITIC

16. Igneous Rocks - Texture
Volcanic eruptions can cause lava to be churned or mixed into a froth (with suds and everything) of lava and gas bubbles
Once solidified, this process forms rocks called Pumice (Felsic) or Scoria (Mafic)
Which one is dark and which one is light? LOOK AT YOUR ESRT!!
The bubbles of gas are called gas bubbles, and when the rock forms it has many gas holes in it! They are called vesicles
This texture is called Vesicular Texture

17. Igneous Rock –Texture ENR:
Porphyritic rocks – mixture of both coarse grains and fine grains
The fine grains make up the rock matrix, which comprises most of the rock
There are larger coarse grains embedded in the matrix though, and these are called phenocrysts
This is the result of 2 cooling periods – first slow, which forms the phenocrysts, and then fast which surrounds them in the matrix
Ex. – a once dormant volcano erupts