Classifying Rocks

1. CLASSIFYI
NG ROCKS

2. The rock of Earth’s crust forms
mountains, hills, valleys, beaches, and
the ocean floor.
When studying a rock sample,
geologists observe the rock’s mineral
composition, color, and texture.

3. Rocks
 What are rocks?
 Rocks are combinations of minerals, rock
fragments, and other material stuck together.
 Minerals (Rice Krispy's)
 Rocks (Rice Krispy's Treats)
 Think of minerals as ingredients…you have
different minerals, you have different rocks.

4. Rocks
 There are many different types of rocks…
 All rocks are classified based on what they are
made from and how they are made.
 Like potatoes: mashed, baked, scalloped, etc.
 Each come from a plain potato, but were made
differently.

5. Rocks are made of mixtures of minerals and
other materials, although some rocks may
contain only a single mineral.

6. 1.Mineral Composition – The type of minerals that
compose the rock.
• There is a list of 20 common minerals that form
most rocks…these minerals are called rock
forming minerals.
What do we examine when looking at
rocks?

7. • Geologists also observe the shape and color
of crystals in a rock to identify its minerals.
• They may perform other tests, such as testing
the surface of a rock with acid, to determine
the presence of certain compounds.

8. 2. Color - A rock’s color provides clues to the
rock’s mineral composition.
• Granite is generally a light colored rock
that has high silica content.
• Basalt is a dark colored rock that is low
in silica.

9. 3. Texture - A rock’s texture, the look and
feel of the rock’s surface, is very useful in
identifying a rock.
• Most rocks are made up of grains,
particles of minerals or other rocks.
• Grains give the rock its texture.
Rough Smooth

10. The size of the grain indicates how
smooth or rough the rock will be.
• Fine Grain – Feel small crystals.
• Coarse Grain – Feel rough
• No Grain – Smooth, like glass.

11. The grain shape can vary widely in
rocks, but can indicate clues to its
formation.
• Particles of Sand
• Small Seeds / Exploding Stars
• Shapes of mineral crystals
• Rock Fragments

12. Patterns can often by seen in rocks
• Flat horizontal layers
• Swirling patterns
• Banded colors
• Random throughout

13. Just like there are different types of potatoes,
there are different types of rocks.
The 3 main types of rocks are:
1. Igneous: Made from cooled lava or magma.
2. Sedimentary: When sediment is squeezed together.
3. Metamorphic: Rocks change under high heat and
pressure.

14. IGNEOUS ROCK
INTRUSIVE
SEDIMENTARY
ROCK
CLASTIC
CHEMICAL
EXTRUSIVE
ORGANIC
METAMORPHIC
ROCK
FOLIATED
NON-
FOLIATED
ROCK
TYPES
INSIDE
EARTH
OUTSIDE
EARTH
Mineral
Bands
NO BANDS
Compaction /
Cementation
Chemical
Reactions
From Living
Organisms