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Igneous Rocks Igneous Rocks

Igneous Rocks - PowerPoint Presentation

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Igneous Rocks - PPT Presentation

Rocks that crystallized directly from a melt Igneous rocks Form as magma cools and crystallizes Rocks formed inside Earth are called plutonic or intrusive rocks Rocks formed on the surface ID: 495624

igneous rocks magma rate rocks igneous rate magma crystals cooling texture felsic grained mafic crystal fast size based glassy

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Slide1

Igneous Rocks

Rocks that crystallized directly from a meltSlide2

Igneous rocks Form as magma cools and crystallizes

Rocks formed inside Earth are called

plutonic

or intrusive rocks

Rocks formed on the surface

Formed from

lava

(a material similar to magma, but without gas

Called

volcanic

or extrusive rocksSlide3

Igneous rocks

Crystallization of magma Fractionation: mineral separation in a magma chamber based on crystallization temperatures

Ions are arranged into orderly patterns

Crystal size is determined by the rate of cooling

Slow rate forms large crystals

Fast rate forms microscopic crystals

Very fast rate forms glass Slide4

Igneous rocks

Classification is based on the rock's texture and mineral constituents

Texture

Size and arrangement of crystals

Types

Fine-grained

– fast rate of cooling

Coarse-grained

– slow rate of cooling

Porphyritic

(two crystal sizes) – two rates of cooling

Glassy

– very fast rate of cooling

Slide5

Classification of igneous rocksSlide6
Slide7
Slide8
Slide9

Mafic magma can become felsic magma as it cools! Bowens Reaction Series tells us that:

As a magma chamber cools, the mafic minerals crystallize first, then felsic ones

As minerals crystallize out, the gas is left behind in the felsic melt…Slide10

The main factor contributing to crystal size is rate of cooling!

Textures based on crystal size:

Aphanitic

: almost no visible crystals

Porphyritic

: large crystals in a matrix of smaller crystals

Phaneritic

: interlocking large crystals

Vesicular

: full of holes (vesicles)

Glassy

: resembles glass

Pyroclastic

: made up of fragments (often ash and pumice)

Slide11

Intrusive (Plutonic)Mafic- roots of plutons

GabbroIntermediate- near the base of plutons

Diorite

Felsic- most plutons (very common!)

GraniteSlide12

Extrusive (volcanic)

Mafic

- shield volcanoes, cinder cones, ocean basalts

Basalt

Scoria

Intermediate- composite cones

Andacite

Dacite

(more felsic)

Felsic- domes and

pyroclastic

deposits

Rhyolite

Tuff

Obsidian and pumiceSlide13

Fine-grained igneous textureSlide14

Course-grained igneous textureSlide15

Porphyritic igneous textureSlide16

Obsidian exhibits a glassy texture