1. Rocks and Minerals

2. What is a Rock? (And why do we study them?)
At first this seems like an easy question. We see rocks every day. But have you really thought about the answer? Each rock is like reading a story. By studying them, observing them, really looking into them, we are “reading” about the history of the earth. A rock is really a lot of different things. Some rocks are shiny, some are flat and dull, and others are very compact. Analyzing these differences can help us understand how they were formed. For us to get the ball rolling, we’ll start by saying that a rock is a mixture or combination of minerals.

3. For Example:
GRANITE

4. Minerals
Every rock, regardless of it’s shape or size, is made up of smaller parts called minerals. A mineral is a naturally occurring chemical compound that has a specific chemical formula.

5. Examples of Minerals
The next few pages will provide details about some common minerals found in rocks. Fill in your data table with as much information as you get from these slides and extra credit will be given for additional information you get through researching on your own. Make your table as complete as possible.

6. Mineral Data Table Common Mineral Features Shape Color Luster Streak
Texture
Hardness
Streak
Reactivity
Magnetism
Other
Quartz
Mica
Feldspar
Talc
Etc.
Your data table also has a brief explanation of the features you will be looking for.

7. Describing Minerals
When studying minerals, the following features should be observed:
Shape – intersection of the crystal faces; many crystals lacked time or room to develop adequately for visual inspection
Color – most obvious; often least useful
Luster – how light reflects off mineral, includes: metallic and nonmetallic (vitreous, pearly, glassy, dull, earthy...)
Texture – is the surface smooth or bumpy, sharp, dull, etc.
Hardness – measured using Moh's scale; 1 (talc - softest mineral) to 10 (diamond- hardest mineral)
Streak – color of minerals powder left on a streak plate
Reactivity – calcite found in limestone and marble reacts readily to acid by fizzing (produces carbon dioxide gas)
Magnetism – attracted to magnet (magnetite) or even acts as a magnet (lodestone)

8. Silicates Minerals composed of a base of Silicon and Oxygen
Mica
- flaky mineral
non-metallic luster
peels into thin layers
Quartz
- hardest common mineral
highly abundant in Earth’s crust
glassy luster
- found in sand, sandstone, granite
Feldspar
most abundant rock-forming mineral
many different colors
Talc
- softest common mineral
white, gray or green color
soapy feel

9. Carbonates Minerals composed of a base of Carbon and Oxygen
Calcite
- fairly soft mineral
white or clear when pure
reacts to acid
found in caves, sea shells, egg
shells and bones
Dolomite
- does not react as readily to acid
found in some limestones and
marbles

10. Iron Oxides Minerals composed of a base of Iron and Oxygen
Hematite
- most common iron oxide
medium hardness
red or silver luster
streak is always red-brown
Magnetite
- dark iron oxide
medium hardness
attracted to a magnet
forms small grains or crystals
in many rocks

11. Iron Sulfides Minerals composed of a base of Iron and Sulfur
Pyrite
- most common sulfide
medium hardness
yellow or gold luster
may form crystals
known as fools gold
Chalcopyrite
- contains copper
tarnishes to iridescent blue, green or purple
medium soft mineral
the major source of copper

12. A Few Others Galena Sulfur - very high lead content bluish grey color
metallic luster
very dense
leading ore for silver
Sulfur
- yellow
very soft
earthy luster
smells like rotten eggs
burns easily
lets off poisonous gas

13. A Few Others, Continued Gypsum Halite Diamond
- clear, white, yellow or red
very soft
many household uses
Halite
rock salt (NaCl)
forms cubes
can be identified by taste
(although not recommended)
Diamond
- made of carbon
hardest mineral

14. And Now … It’s Time to Rock
We have a basic understanding of what rocks are made of, now let’s look at HOW they are made. And HOW rocks are formed is the basis for our three rock groups.
Igneous
Sedimentary
Metamorphic

15. Igneous Rocks
Igneous rocks make up 95% of the rocks in the Earth’s crust. They are also some of the oldest rocks that are found at the surface of Earth. Igneous rocks form from molten rock, which is either ejected at the surface of the Earth, or that cools off underground. When volcanoes erupt, they can eject molten rock, as shown in the photo. Igneous rocks are sub divided into two types of classifications (based on where they form): Extrusive and Intrusive.

16. Extrusive Igneous Rocks
Extrusive igneous rocks form when molten rock reaches the earth's surface and cools. Air and moisture cool the lava rapidly. The quick cooling doesn't allow the formation of large crystals, so most extrusive rocks have small crystals or none at all. In some extrusive rocks, like pumice and scoria, air and other gases are trapped in the lava as it cools. We can see holes remaining in the rock where the bubbles of gas were located.

17. Extrusive Examples Basalt Obsidian Pumice - the most common extrusive
eroded basalt creates
the black sand beaches
Obsidian
cools EXTREMELY quickly
no crystals
has a glassy surface
Pumice
- cooled off VERY quickly
associated with gaseous
eruptions
lightweight
no crystals
some forms can float

18. Intrusive Igneous Rocks
Intrusive igneous rocks form from magma that cools before it even reaches the Earth’s surface. Molten rock that is still underground is called magma. Molten rock that cools before it reaches the surface hardens to become intrusive igneous rock. Because it forms deep beneath Earth's surface, it has more time to cool and it develops large crystals.

19. Intrusive Examples Diorite Gabbro Granite Medium to coarse grained
quite rare
Gabbro
medium to coarse
grained
exceedingly variable
found on the moon
Granite
- medium to coarse grained
light to dark in color
made of feldspar and quartz

20. Extrusive vs. Intrusive Formation

21. Sedimentary Rocks
Sedimentary rocks were formed from sediment that came from the weathering and erosion of other rocks. They can be formed from igneous, sedimentary and metamorphic rocks that have been broken down by weathering. Small rocks, fragments and organic remains that have been moved by water, wind or other agents of erosion are called sediment. Over a period of time, sediment is cemented together to form a solid mass, now known as sedimentary rock. In nature sedimentary rocks are usually found in layers with the oldest layer on the bottom. Sedimentary rocks are sub divided into three types of classifications: Clastic, Chemical and Organic.

22. Sedimentary Clastic Rocks
Clastic sedimentary rocks were formed from rocks that have been broken down into fragments by weathering, which then have been transported and deposited elsewhere. The word clastic comes from the Greek word klastos which means "broken."

23. Clastic Examples Conglomerates Shale Sandstone large rock pieces that
are cemented together
can break apart
easy to see what it is
made of
Shale
made of very fine
grains of clay
very smooth
breaks easily
Sandstone
made of fine grains of sand
cemented together
sand can rub off of the rock

24. Sedimentary Chemical Rocks
Chemical sedimentary rocks are the result of chemical deposits, usually formed when water evaporates and leaves minerals behind. Sedimentary rocks that result from chemical deposits are called chemical rocks.

25. Chemical Examples Halite Cave Formations often found where
lakes or seas have
dried up
can be found in
various colors
Cave Formations
formed by water
dripping and carrying
minerals downward

26. Sedimentary Organic Rocks
The third form of sedimentary rocks are known as Organic rocks. These are formed from the life processes of living organisms or the remains of the organisms. These remains settle over time and become cemented together forming a new rock.

27. Organic Examples Coal Some Limestones formed from plants that
died in swamps years ago
a very important fossil fuel
Some Limestones
formed from the shells of clams
can be from ancient sources
Note: some limestones are considered
Chemical Rocks

28. creates two categories:
Metamorphic Rocks
Rocks that have changed shape or composition due to intense heat and pressure are called Metamorphic rocks. Metamorphic rocks can be created from sedimentary, igneous or other metamorphic rocks. They are formed deep inside the earth where sit under intense heat and pressure from the rock above.
The texture of
metamorphic rocks
creates two categories:
Foliated and
Non-foliated.

29. Foliated Metamorphic Rocks
In foliated metamorphic rocks, the composition of the original rock is not apparent. This is because the heat and pressure have, in a sense, recombined the contents of the rock to form different minerals. The individual mineral grains may recrystallize to form larger crystals that make parallel bands or lines across the rock. Notice the foliation (or lines) in the examples that follow.

30. Foliated Examples Slate Schist Gneiss made from heat and
pressure on shale
Schist
made from heat and
pressure on basalt
Gneiss
made from heat and pressure
on granite

31. The crystals in non- foliated rocks combine and rearrange so they don’t form any bands. Marble is an example

32. But Weeping Angels are aliens and not made of marble … not a very good example, after all!

33. Non-foliated Metamorphic Rocks
Marble is formed from limestone, which is formed from calcite. Even though limestone and marble are made of the same thing, a sculptor would never use limestone for a project. Marble is used because it is compact and has bigger crystals from all of the heat and pressure. It is going to hold together for a lot longer than the limestone would.

34. Non-foliated Examples
Quartzite
made from heat and
pressure on sandstone
Marble
made from heat and
pressure on limestone

35. Now, Did you Get All of That?
Take THIS QUIZ to see how you do in distinguishing between the different rock types. If you do not score at least 10, review over the rocks and try again. Do not move on until you can get at least 10 correct answers!