Chapter 4

Bomb- a pyroclast 2mm or larger that consists of a blob of lava that cools in flight and becomes rounded, or a chunk torn loose from previously solidified volcanic rock

Concordant intrusion- an igneous intrusion whose boundaries lie parallel to layers of bedded country rock

Decompression melting- the spontaneous melting of rising mantle material as it reaches a level where pressure decreases below a critical point, without the induction of any additional heat

Dike- a sheetlike discordant igneous intrusion that cuts across layers of bedded country rock

Discordant intrusion- an igneous intrusion that cuts across the layers of igneous rock it intrudes

Extrusive igneous rock- a fine-grained or glassy igneous rock formed from magma that erupts at earth’s surface as lava cools rapidly

Felsic Rock- light-colored igneous rock that is poor in iron and magnesium, but is rich in high-silica minerals such as: quartz, clase feldspar, plagioclase feldspar

Fractional crystallization- the process by which the crystals formed in the cooling of magma are segregated from the remaining liquid rock, usually by settling to the floor of the magma chamber

Intermediate rock- between felsic and mafic, midway composition

Intrusive igneous rock- a coarse-grained igneous rock that formed from magma and is deep inside the earth’s crust. Cooled slowly

Lava- magma that flows onto the earth’s surface

Mafic rock- dark-colored igneous rock containing minerals such as pyroxenes and olivines that are rich in iron and magnesium and poor in silica

Magma chamber- a large pool of magma that forms in the lithosphere as rising magmas melt and push aside surrounding solid rock

Magmatic differentiation- a process by which rocks of varying composition arise from a uniform parent magma as various minerals are withdrawn from it by fractional crystallization as it cools, changing its composition

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

Pluton- a large igneous intrusion, ranging in size from a cubic kilometer to hundreds of kilometers. Forms deep in the earth’s crust
Pyroclast- a rock fragment ejected into the air by a volcanic eruption

Sill- a sheet like concordant igneous intrusion formed by the injection of magma between layers of bedded country rock

Ultramafic rock- an igneous rock composed of primarily mafic minerals and containing less than 10 percent feldspar

Volcanic ash- pyroclasts usually less than 2mm in diameter, usually glass, that form when escaping gases form a fine spray of magma from a volcano

Chapter 5: Sedimentary Rocks

Carbonate Rock- a sedimentary rock formed from carbonate sediment

Carbonate sediment- a sediment formed from the accumulation of carbonate minerals directly or indirectly precipitated by marine organisms

Cementation- a diageneric change in which minerals are precipitated in the pores between sediment particles and bind them together

Chemical weathering- weathering in which the minerals in a rock are chemically altered or dissolved

Compaction- a diagenetic decrease in the volume and porosity of a sediment as its particles are squeezed closer together by the weight of overlying sediments

Conglomerate- a sedimentary rock composed of pebbles, cobbles, and boulders; the lithified equivalent of gravel

Cross-bedding- a sedimentary structure consisting of beds deposited by currents of wind or water and inclined at angles as much as 35 degrees from the horizontal

Crude Oil- an organic substance formed by diagenesis from organic material in the pores of sedimentary rocks; a diverse class of liquids composed of complex hydrocarbons. Also called petroleum

Diagenesis- the physical and chemical changes caused by pressure, heat, and chemical reactions, by which buried sediments are lithified to form sedimentary rocks

Evaporate rock- a sedimentart rock formed