ThursdayJanuary 20, 2011

(Igneous Rocks)

The Launch PadThursday, 1/20/11

Which types of rocks can be weathered into sediment?

Igneous, metamorphic, or even sedimentary rocks can all be weathered into sediment.

Describe the process of lithification.Lithification occurs when sediment is deposited in layers, which are compacted by the weight of the

layers above. The pressure on the sediment layers cement them into sedimentary rocks.

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WS – The Rock Cycle 1/19 1/21

Igneous Rocks Igneous rocks form as magma

cools and crystallizes.

Rocks formed on the surface are formed from lava (a

material similar to magma, but without gas) are called volcanic or extrusive rocks.

Rocks that are formed inside the Earth are called plutonic

or intrusive rocks.

Igneous Rocks When magma crystallizes, its ions are arranged into

orderly patterns. The size of the crystal is

determined by the rate of cooling.

Slow cooling rates form large crystals.

Fast cooling rates form microscopic crystals.

Very fast cooling rates form glass.

Igneous Rocks Classification of igneous rocks is based on the rock’s texture

and mineral constituents. Texture refers to the size and arrangement of the crystals in the rock.

Types of igneous rock textures: Coarse-grained – slow rate of cooling

Fine-grained – fast rate of coolinggranite andesite

Igneous Rocks Classification of igneous rocks is based on the rock’s texture

and mineral constituents. Texture refers to the size and arrangement of the crystals in the rock.

Types of igneous rock textures:Glassy – very fast rate of cooling

Porphyritic (two crystal sizes) – two rates of cooling

obsidian pumice porphyritic granite

Figure 3.5

Figure 3.5 A

Figure 3.5 B

Figure 3.5 D

Glassy (obsidian)

Figure 3.7

Figure 3.8 pumice

Igneous Rocks Mineral composition is, of course, the types of

minerals that make up the rock.

The crystallization of magma is explained by Bowen’s Reaction Series, which shows the order

of mineral crystallization.

This is influenced by crystal-settling in the magma.

Bowen’s Reaction Series is shown on the next slide.

Figure 3.13

Bowen’s reaction series

Bowen’s Reaction SeriesMagma, with its diverse chemistry, crystallizes

over a temperature range of a t least 200oC.

Therefore, as magma cools, certain minerals crystallize first, at relatively high temperatures.

At successively lower temperatures, other minerals crystallize.

This arrangement of minerals became known as Bowen’s Reaction Series.

Bowen’s Reaction SeriesThe first mineral to crystallize from a mass

of magma is olivine.

Further cooling results in the formation of pyroxene, as well as plagioclase feldspar.

At intermediate temperatures, the minerals amphibole and biotite begin to

crystallize.

Bowen’s Reaction SeriesDuring the last stage of crystallization,

after most of the magma has solidified, the minerals muscovite and potassium

feldspar may form.

Finally, quartz crystallizes from any remaining temperature.

Bowen’s Reaction SeriesIn nature, we find that minerals that form in the

same general temperature range on Bowen’s chart are found together in the same igneous

rocks.

For example, the minerals quartz, potassium feldspar, and muscovite are typically found

together as major components of the igneous rock granite.

Figure 3.13

Bowen’s reaction series

Worksheet

Igneous Rocks(Part 1)