3.2 Rocks group

8/17/2019 3.2 Rocks group

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Ms. Hartnett's Earth Science 1

Rocks – a rock is a collection of one or more minerals.


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Rock facts1. Most rocks have a number of minerals in common. In other

words, only a small number of minerals are very common.2. Most rocks are heterogeneous. This means that they are made of

two or more different minerals and are not the same throughout.

3. Some (very few) rocks are homogeneous or monominerallic.

This means that they are made of only one type of mineral andthey are the same throughout.

4. Rocks are divided into 3 major classes. They are sedimentary,

igneous, and metamorphic.

5. Rocks are classified by how they formed or origin.

6. Structure, texture, and composition (what a rock is made of) helpus to figure out the environment that the rock formed in (origin).


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Igneous Rocks – rocks formed from the cooling andsolidification of molten materials (magma). Whenever lava

cools, an igneous rock forms.

There are two sub-classes of igneous rocks:

1. Intrusive/Plutonic – igneous rocks that cooled and solidified

beneath the Earth’s surface (The magma cools underground).

These rocks take a very long time to cool because they are not onthe surface. Because they take a longer time to cool, they end up

having large crystals/grains.

2. Extrusive/Volcanic – igneous rocks that cooled and solidified on

the Earth’s surface. Lava on the surface cools to form igneous

rocks. These rocks cool very quickly and have very small

crystals/grains or none at all (glass).


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Sedimentary Rocks – rocks that formed from the accumulationof deposited rock particles, fragments, and organic material

underwater. (Remember, they are deposited in horizontal layers)?

There are 3 basic categories of sedimentary rocks:

1. Clastic – the rock fragments are lithified (glued) together to

form a rock. These rocks are made of different pieces stuck

together. Conglomerate and Breccia have the largest particles.

2. Crystalline/Chemical - rocks that formed from ions (smallest

particles) that were dissolved in the sea water. These rocks

usually form as the ocean water evaporates away and leaves

the dissolved minerals behind. These are also monominerallic.

3. Bioclastic/Organic – rocks formed from biologic products.

(Things that died and solidified together over time. Coal and

limestone are great examples.


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Metamorphic Rocks – rocks that have been changed by theaction of heat and pressure from occurrences inside the Earth.

Metamorphic rocks were once sedimentary, igneous, or adifferent type of metamorphic rock. Because of the heat

and pressure of magma coming in contact with rock, the

former rock changes into a new one.

The rock does not melt while it changes into a metamorphic, but

it almost does. It just deforms and distorts. What kind of rock

would form if rock melted and then re-cooled? ______________

There are two groups of metamorphic rocks:1. Foliated – alignment of minerals in paper thin layers or bands.

2. Non-foliated – no alignment of minerals.


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3.2 Rocks group