Chapter 5

Question 1

igneous rock

Answer 1

begins in the lower crust or upper mantle melts to form magma, which rises up through the crust

Question 2

extrusive igneous rock

Answer 2

forms from solidified lava or ash

it comes out onto the surface

Question 3

intrusive igneous rock

Answer 3

magma that never reaches the surface and solidifies underground

Question 4

shapes of intrusive igneous rock

Answer 4

plutons: massive blobs
batholiths: the largest of the plutons
dikes: thin sheet cutting across layering in the wall rock
sills: form parallel to the layers of wall rock

Question 5

determining igneous rock types

Answer 5

grain size
color
specific gravity

Question 6

texture

Answer 6

the size, shape, and arrangement of its grain

Question 7

crystalline

Answer 7

specimens composed of interlocking grains

Question 8

glasses

Answer 8

rocks that are shiny and contain no grains

Question 9

porous

Answer 9

rocks that have sponge-like masses

Question 10

fragmented

Answer 10

rocks that appear to have pieces cemented together

Question 11

cooling rate

Answer 11

most important factor controlling grain size - the slower a magma cools, the more ions have to migrate to crystal seeds; the faster it cools the less time there is and the smaller the grains will be

Question 12

viscosity

Answer 12

resistance of material to flow

the less viscous the more fluid the easier it is for ions to migrate and larger crystals can become

Question 13

Four Major Compositional groups of Igneous Rocks

Answer 13

1. ) Felsic
2. ) Intermediate
3. ) Mafic
4. ) Ultramfic

Question 14

Felsic

Answer 14

ex: feldspar and silica and quartz
have the most silica and the least iron and magnesium
light colored and have low specific gravities

Question 15

Intermediate

Answer 15

chemical compositions, colors, specific gravities, and mineral assemblages between those of felsic and mafic rocks

Question 16

Mafic

Answer 16

have much less silica, potassium, and sodium than felsic rocks but much more calcium, iron, and magnesium
dark green or black and have higher specific gravities

Question 17

Ultramafic

Answer 17

least amount and the most iron and magnesium but very little aluminum, potassium, sodium, or calcium
very dark and have highest specific gravities of igneous rocks

Question 18

Decompression melting

Answer 18

stretching of the lithosphere at a divergent plate boundary (ocean ridge) or continental rift lowers the confining pressure on the asthenosphere and allows the heat in the rocks to overcome the bonds and cause melting
requires no additional input of heat

Question 19

Flux melting

Answer 19

water and other volatiles are released from these minerals when the subducted plate reaches critical depth and risse into the asthenosphere where they help melt it
no additional heat required

Question 20

shield volcanoes

Answer 20

made mostly of highly fluid lava
broad structures with gentle slopes
largest types of volcanoes

Question 21

Lava domes

Answer 21

much smaller than shield volcanoes with extremely viscous lava
steeper slopes than shield volcanoes

Question 22

Cinder cones

Answer 22

made mostly from relatively fine-grained pyroclastic material and form above
smaller than shield volcanoes and moderate slopes

Question 23

stratovolcanoes

Answer 23

made of large amounts of both lava and pyroclastic material
have the steepest slopes
commonly found in subduction zones
explosive eruptions

Question 24

lahars

Answer 24

mudslides made of volcanic ash, water, and debris