What are the three types of rocks

Igneous, sedimentary, and metamorphic are the three main groups of rocks.. Igneous Rocks– rocks that form from hot magma molten rock when it cools and solidifies... Chemical Chrystalin

Aim: What are the three types of rocks?

I Rocks – made up of more than one mineral Rocks are

classified according to how they were formed Igneous,

sedimentary, and metamorphic are the three main groups of rocks.

A Igneous Rocks– rocks that form from hot

magma (molten rock) when it cools and solidifies.

2 Rate of cooling can be determined by crystal size.

a Intrusive igneous rocks - have large crystals due to

the slow cooling of magma inside the earth.

b Extrusive Igneous Rocks – have small crystals

due to the fast cooling of lava on the earth’s

surface.

3 Igneous rocks are classified according to crystal size and color

a Felsic igneous rocks – light in color, low in

density, and rich in feldspar and silica.

b Mafic igneous rocks – dark in color, high in

density, and rich in magnesium and iron.

Granite – coarse texture

Rhyolite – Fine texture

Andesite – Fine texture

Obsidian – Glassy Texture

B Sedimentary Rocks – rocks that are formed by the

hardening and cementing of layers of sediments.

1 Three types of Sedimentary Rocks

a Clastic – rocks formed from fragments of

other rocks Ex: shale, sandstone, conglomerate.

b Chemical (Chrystaline) – rocks formed from mineral grains that fall out of a solution

(precipitate) by evaporation or chemical reaction Ex: rock salt and limestone.

c Organic – rocks formed from the remains of plants and animals Ex: coal and limestone made of shell

fragments

2 Characteristics of Sedimentary Rocks

a Have layers (stratification)

b Contain fossils (remains, impressions, or any other

evidence of plants and animals preserved in rock.

Conglomerate rocks are sedimentary rocks They are made up of large sediments like sand and pebbles The sediment is so large that pressure alone cannot hold the rock together; it is also cemented together with dissolved minerals.

Sandstone rocks are sedimentary rocks made from

small grains of the minerals quartz and feldspar They often form in layers as seen in this picture They are often used

as building stones

Shale rock is a type of sedimentary rock formed from clay that is compacted together by pressure They are used to make bricks and other material that is fired in a kiln.

Limestone rocks are sedimentary rocks that are made from the mineral calcite which came from the beds of

evaporated seas and lakes and from sea animal shells This rock is used in concrete and is an excellent building stone for humid regions

Gypsum rocks are sedimentary rocks made up of

sulfate mineral and formed as the result of evaporating sea water in massive prehistoric basins It is very soft and is used to make Plaster of Paris, casts, molds, and wallboards.

3 Metamorphic Rocks – rocks that have been

exposed to great heat and pressure.

a Dynamic (Regional) Metamorphism – large areas

of rock under great heat and pressure (mountain

building)

b How heat and pressure causes rocks to change:

•Pressure squeezes grains closer together causing

c Thermal (Contact) Metamorphism – igneous

intrusions bake overlying rock The changes in the rock are less drastic than regional metamorphism and foliation is not produced.

d Characteristics of Metamorphic Rocks:

•Foliation – grains are in parallel layers Ex: slate

•Banding – bands of light colored minerals

alternate with bands of dark colored minerals.

Gneiss is a high grade metamorphic rock This means that gneiss has

been subjected to more heat and pressure than schist Gneiss is coarser than schist and has distinct banding This banding has alternating layers that are composed of different minerals The minerals that compose

gneiss are the same as granite Feldspar is the most important mineral

Quartzite is composed of sandstone that has been metamorphosed

Quartzite is much harder than the parent rock, sandstone It forms from sandstone that has come into contact with deeply buried magmas

Quartzite looks similar to its parent rock The best way to tell quartzite

Slate is a fine-grained metamorphic rock with perfect cleavage that

allows it to split into thin sheets Slate usually has a light to dark brown streak Slate is produced by low grade metamorphism, which is caused

by relatively low temperatures and pressures

Slate has been used by man in a variety of ways over the years One use for slate was in the making of headstones or grave markers Slate is not very hard and can be engraved easily The problem with slate though is its perfect cleavage The slate headstones would crack and split along these cleavage planes This is not a desirable attribute for a head stone Slate was also used for chalk boards The black color was good as a

background and the rock cleaned easily with water Today it is not very

Schist is a medium grade metamorphic rock This means that it has been

subjected to more heat and pressure than slate, which is a low grade

metamorphic rock As you can see in the photo above schist is a more coarse grained rock The individual grains of minerals can be seen by the naked eye Many of the original minerals have been altered into flakes Because it has been squeezed harder than slate it is often found folded

Marble is metamorphosed limestone or dolomite Both limestone and

dolomite have a large concentration of calcium carbonate (CaCO3)

Marble has many different sizes of crystals Marble has many color

variances due to the impurities present at formation Some of the

different colors of marble are white, red, black, mottled and banded,

gray, pink, and green

Marble is much harder than its parent rock This allows it to take a polish which makes it a good material for use as a building material, making sink tops, bathtubs, and a carving stone for artists Today, headstones are made from marble and granite because both of these rocks weather very slowly and carve well with sharp edges