Igneous Rock

Question 1

Andesite

Answer 1

a volcanic rock type intermediate in composition between rhyolite and basalt. Extrusive equivalent of diorite

Question 2

Basalt

Answer 2

a fine grained dark mafic igneous rock composed largely of plagioclase feldspar and pyroxene. The extrusive equivalent of gabbro.

Question 3

Bomb

Answer 3

That thing she showed in class?

Question 4

Country rock

Answer 4

The rock surrounging an intrusive igneous rock.

Question 5

Dacite

Answer 5

A light-colored, fine grained extrusive igneous rock with the same general composition as andesite. The extrusive equivalent of grandodiorite.

Question 6

Decompression melting

Answer 6

Melting that occurs when mantle material rises to an area of lower pressure at a mid-ocean ridge. As the mantle material rises and the pressure decreases below a critical point, solid rocks melt spontaneously, without the introduction of any additional heat.

Question 7

Extrustive igneous rock

Answer 7

A fine-grained or glassy igneous rock formed from a rapidly cooled magma that erupts at the surface through a volcano.

Question 8

Felsic rock

Answer 8

Light colored igneous rock that is poor in iron and magnesium and rich in high silica minerals such as quartz, orthoclase feldspar, and plagioclase feldspar.

Question 9

Fluid-induced melting

Answer 9

Melting that takes place when water-laden sediments on a subducting oceanic plate are carried downward into the subduction zone. The increase in pressure squeezes water out of the minerals in the out layers of the descending slab. The water rises buoyantly into the mantle wedge above the slab. Because water lowers the melting temperature of rock, it induces melting in the mantle wedge.

Question 10

Fractional crystallization

Answer 10

The process by which the crystals formed in a cooling magma are segragated from the remaining liquid at progressively lower temperatures.

Question 11

Gabbro

Answer 11

A dark gray, coarse-grained intrusive igneous rock with an abundance of mafic minerals, particularly pyroxene. The intrusive equivalent of basalt.

Question 12

Intermediate igneous rock

Answer 12

An igneous rock midway in composition between mafic and felsic, neither as rich in silica as the felsic rocks nor as poor as the mafic rocks.

Question 13

Intrusive igneous rock

Answer 13

A coarse-grained igneous rock that crystallized slowly when magma intruded into country rock deep in Earth’s crust.

Question 14

Mafic rock

Answer 14

A dark-colored igneous rock containing minerals (pyroxenes, olivines) rich in iron and magnesium and relatively poor in silica.

Question 14

Magma chamber

Answer 14

A magma-filled cavity in the lithosphere that forms as ascending drops of melted rock push aside surrounding solid rock.

Question 15

Magmatic differentiation

Answer 15

A process by which rocks of varying composition can arise from a uniform parent magma. Varyious minerals crystallize at different temperature and the composition of the magma changes as it is depleted of the chemical elements withdrawn to make the crystallized minerals.

Question 16

Obsidian

Answer 16

A dense, dark, glassy volcanic rock usually of felsic composition.

Question 17

Partial melting

Answer 17

The incomplete melting of a rock that occurs because the minerals that compose it melt at different temperatures.

Question 18

Pegmatite

Answer 18

A vein of extremely coarse grained ganite, crystallized from a water-rich magma in the late stages of solidification, that cuts across a much finer grained country rock. Pegmatites provide ores of many rare elements, such as litium and beryllium.

Question 19

Peridotite

Answer 19

A coarse-grained ultramafic intrusive ineous rock composed of olivine with small amounts of pyroxene and amphibole. The dominant rock in Earth’s mantle and the source rock of basaltic melts.

Question 20

Pluton

Answer 20

A large igneous intrusion rnaging in size from a cubic km to hundreds of cubic km, formed at depth in the crust.

Question 21

Porphyry

Answer 21

A lava of mixed texture in which large crystals “float” in a predominantly fine crysalline matrix.

Question 22

Pumice

Answer 22

A frothy mass of volcanic glass with a great number of holes (vesicles) that remain after trapped gas has escaped from the solidifying melt..

Question 23

Pyroclast

Answer 23

A volcanic rock fragment ejected into the air during eruption.

Question 24

Rhyolite

Answer 24

A light-brown to gray, fine-grained extrusive igneous rock with a felsic composition. The extrusive equivalent of granite.

Question 25

Sill

Answer 25

A sheet like concordant intrusion formed by the injection of magma between parallel layers of preexiting bedded rock.

Question 26

Stock

Answer 26

An irregular mass of coarse-grained igneous rock less than 100km in area.

Question 27

Tuff

Answer 27

Any volcanic rock lithified from pyroclasts.

Question 28

Ultramafic rock

Answer 28

An igneous rock consisiting primarily of mafic minerals and containing less than 10% feldspar.

Question 29

Vein

Answer 29

A sheetlike deposit of mineral precipitated in fractures or joints that are foeign to the host rock.

Question 30

Viscosity

Answer 30

A measure of a fluid’s resistance to flow.

Question 31

Volcanic ash

Answer 31

Extremely small fragments, usualy of glass that form when escaping gases force a fine spray of magma from a volcano.