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

Rocks are classified by how they formed or origin.. Hartnett's Earth Science 4 Sedimentary Rocks – rocks that formed from the accumulation of deposited rock particles, fragments, and org

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

Ms Hartnett's Earth Science

2

Rock facts

1 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 and they 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) help

us to figure out the environment that the rock formed in (origin)

Ms Hartnett's Earth Science

4

Sedimentary Rocks – rocks that formed from the accumulation

of 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

Ms Hartnett's Earth Science

6

Igneous Rocks – rocks formed from the cooling and

solidification 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 on the 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)

Ms Hartnett's Earth Science

8

Metamorphic Rocks – rocks that have been changed by the

action of heat and pressure from occurrences inside the Earth

Metamorphic rocks were once sedimentary, igneous, or a different 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.