Igneous Rocks
Sire Kassama2014
Igneous: granite, basalt, crystallize from hot molten rock
There are two main types of igneous rock: intrusive and extrusive
Meteorites; igneous rocks from space Cinder: small chunks of rock about the size
of a grape that solidify in the air; full of holes made by gas bubble
Intro to Info
Igneous rock never contain fossils and are normally hard
Volcanic bombs happen when small pieces of lava blast through air at high speed and cool very rapidly, most turn to volcanic ash and some form pumice which is light enough to float on water
Intro To Info
Phaneritic: size of grains are large enough to see unaided; characterized by slow cooling in plutonic environment
Aphanitic: grain size is too small to see with naked eye; characterized by rapid cooling in volcanic environments
Porphyritic: rock has distinct differences in the size of crystals
Igneous Grain Size
Any igneous rock made on the surface of the volcano
Grains are too small to see because magma cooled quickly on earth’s surface and crystals do not have time to grow large and call these rocks fine grained
Sometimes lava cools so rapidly that no crystals grow and instead the lava turns to a glass like rock called obsidian or volcanic glass
Examples: rhyolite, andesite, obsidian
Extrusive Igneous Rocks
Also known as Plutonic Rocks Any igneous rock made underground Characterized by coarse grains in rocks Crystal minerals are large enough to see
because magma cools slowly which gives crystals time to grow and call these rock coarse grained
Examples include: granite, gabbro, diorite
Intrusive Igneous Rocks
Extrusive vs. Intrusive Igneous Rocks
Intrusive Extrusive
Cooled and solidified at a considerable depth
Visual appearance reveals interlocking crystals forming the rock mass
Characterized by large crystal sizes Cooling and hardening is typically
quite slow Surface feels relatively rough
Characterized by fine-grained textures
Formed at or above the surface of the planet
Cooling and hardening is typically quite rapid
Surface feels relatively smooth
Both• Silica is the most abundant component• Named and identified on the basis of composition and texture • Formed from the crystallization of minerals• Contain feldspar minerals• May become transformed into sedimentary rocks when exposed to the Earth’s surface
Identifying Igneous Rocks
Rock Grain Size Color
Granite Coarse Light
Gabbro Coarse Dark
Pegamite Very coarse Light and dark
Basalt Fine Dark
Rhyolite Fine Light
Andesite Fine Medium
The diagrams below show the crystals of four different rocks viewed through the same hand lens. Which crystals most likely formed from molten material that cooled and solidified most rapidly?
ROCK NAME TYPE ( Igneous, Sedimentary, metamorphic) FORMATION Igneous (Extrusive, Intrusive) (volcanic, plutonic) (felsic or mafic) Sedimentary ( Clastic, chemical, biochemical, organic) Metamorphic (Regional, Contact Metamorphism) (low grade-high grade) ENVIRONMENT TEXTURE Igneous (phaneritic, aphanitic, porphyritic) Sedimentary (grain size) Metamorphic Foliated or non-foliated HARDNESS RANGE MINERALS PHYSICAL DESCRIPTION (Color) USES OTHER PROPERTIES
Need To Know on Rocks
A Few Igneous Rocks
Is an extrusive igneous rock Forms from Felsic Found where there are explosive volcanoes
along subduction boundaries Has small crystals
Andesite
Is intrusive igneous rock Sometimes called black granite Could occur as dikes or sills as it hardens
in the ground Normally dark and mottled in appearance Minerals: plagioclase and hornblende It’s extrusive form is andesite Hardness: 7
Diorite
It is the most abundant of Earth’s Volcanic Rocks and major component of ocean’s crust
Fine grained Dark colored Low viscosity (runny) Moon’s dark patches Minerals: augite and
plagioclase
Common extrusive igneous rock
Made from solidified lava
Sometimes made from volcanic bombs
Hardness: 6-7
Basalt
Extrusive igneous rock Degrades over time Black and sharp with
frosted glassy surface Used for surgical
blades but was once important in ceremonial and sacrificial knives
Found in young lava flows
Minerals: quartz and feldspar
Hardness: 5.5 Often found with
pumice
Obsidian
Intrusive Igneous Rock Forms from mafic type magma Is the intrusive form of basalt Normally very dark color Commonly made into countertops
Gabbro
Extrusive igneous rock Made from thick sticky lava
Rhyolite
Igneous rock sometimes containing crystals of beryl and garnet
Pegamite
Igneous Rock Some giant stones of Stonehenge are
dolerite
Dolerite
Intrusive igneous rock Made of mostly quartz, feldspar and mica Pink and white; coarse grained rock Found in India, Italy, US Used in Mt. Rushmore and buildings Appears in huge bubbles of cooling magma
called batholiths Hardness: 6
Granite
Extrusive igneous rock Vesicular because gases escaped from the
lava when cooled
Scoria
Extrusive Igneous Rocks
Has volcanic origin vesicular because
gases escaped from the lava when cooled
Can be related to rhyolite with its composition
Used to make building blocks, concrete, toothpaste, cosmetics, and soap
Can float in water Often found with
obsidian Hardness: 6
Pumice
The following questions and answers are from the New York State Regents Website: http://www.regentsprep.org/Regents/core/questions/topics.cfm?Course=ESCI
Geology.com
Other Resources