1. Petrology/geology = study of rocks

2. Rocks are the record of our planet’s past…interesting
where rivers used to flow
where huge inland seas were located
what lived in these waters
stories of glaciers and how an ice age changed the planet
ancient climates

3. What is a ROCK? --start your study guide
A MIXTURE of minerals (and sometimes organic matter, like shells)
Example: look at granite
quartz (35%)
mica (10%)
feldspar & (hornblend) (55%)
Note: ratio can vary a bit
Rocks are NOT elements or compounds.

5. What minerals make up other rocks? (don’t memorize)
Basalt —pyroxene, olivine, augite, feldspar
Marble —dolomite or calcite
Rock salt —halite
Sandstone —quartz and feldspar
Limestone —mostly calcite
Diorite —feldspar, hornblende, mica, quartz
Gabbro —feldspar, augite, olivine
Rhyolite —quartz, feldspar, hornblende, mica
Andesite —feldspar, hornblende, mica

6. How geologists classify and identify rocks:
1. Texture
2. Composition
3. Origin

7. 1. Texture (look at the grains)—are the grains large/small, smooth/pointy, glassy, smooth, chalky, etc?
b. Grain shape
smooth and rounded (like conglomerate)
jagged (breccia)
c. Grain pattern
wavy, swirling pattern
flat layers
rows of multicolored bands(ex: gneiss)
random pattern
a. Grain size
(1) coarse-grained= can be seen without microscope
(2) fine-grained= only seen with microscope
(3) no crystals/grains because it formed too quickly (smooth & shiny like obsidian)

9. 2. Mineral composition (what the rock is made of)
Ex: Limestone
95% calcite
5% aragonite
scientists look a very thin slice under microscope and do tests
acid test
look for rocks that have calcite
magnet test
look for iron or nickel

10. Origin of the rock (how & where did the rock FORM?)
1. Igneous (intrusive & extrusive—we’ll talk more about the 2 types later)
forms when molten material (magma/lava) cools and hardens
can form at surface or underground
Ex: granite, basalt, pumice, obsidian

11. 2. Sedimentary (clastic, chemical & organic-we’ll talk about the 3 types in more detail later)
Usually form under water & have layers
Particles called sediment (ex: pieces of rock, mud, sand, shells and dust) cemented and/or pressed together by pressure above
takes millions of years
most rocks (3/4) on earth are sedimentary
Ex of sedimentary rocks: sandstone, shale, limestone
Some sedimentary rock have fossils from extinct animals/plants (paleontology).

12. 3. Metamorphic
due to extreme heat, pressure, and/or chemical reactions DEEP underground
over 10 km deep °C
Ex: slate, schist, and marble

13. Questions Which type of rock forms the fastest? What is a ROCK?
>>volcanic (extrusive) igneous
What is a ROCK?
>>mixture of minerals (sometimes contains organic material)
What forces on Earth cause rocks to form?
>>heat, pressure
What can rocks tell us about the Earth’s past?
>>age, what lived, climate, forces
List the 3 BASIC types of rocks.
>>igneous, metamorphic, sedimentary
What is the study of rocks called?
>>petrology (type of geology)

14. Questions:
Which kinds of rock forms from material that settles on the ocean floor?
>>sedimentary
Molten rock beneath Earth’s surface is called _______.
>>magma
Which type of rock is MOST LIKELY to form layers?
How do scientists classify rocks?
>>according to the way they were formed (origin), as well as their texture and mineral composition