Chap 4 Quiz, Volcano's and Igneous Rocks

Pyroclastic igneous rock forms from _____. a. viscous lava flows b. rapidly cooling plutons c. basalt and gabbro d. explosive volcanic activity e. melting of country rock

Explosive volcanic activity

A key characteristic of igneous rocks is that they _____. a. always contain more than three different mineral types b. are made up of minerals that crystallized from molten rock matter called magma c. are the youngest rocks on Earth d. are not as hard as sedimentary rock e. never contain iron or magnesium

Are made up of minerals that crystallized from molten rock matter called magma

An igneous rock with no visible crystals _____. a. slowly on the Earth's surface b. cooled quickly in a magma chamber c. has a phaneritic texture d. is granite e. cooled quickly on Earth's surface

Cooled quickly on Earth's surface

Most lava temperatures are taken at volcanoes that show little or no explosive activity because _____. a. these volcanoes are extremely common and therefore more intresting b. these volcanoes are extremely rare and therefore more intresting c. explosive volcanoes cannot be approached safely d. their malfic flows give more accurate average temperatures e. their felsic flows give more accurate average temperatures

Explosive volcanoes cannot be approached safely

Bowen's reaction series explains the order of mineral formation with decreasing pressure. True or False

False

Crystal settling involves gravitational settling of melted minerals. True or False

False

Magmas with the highest percentages (>65%) of silica are called _____. a. ultrafelsic b. ultramafic c. felsic d. mafic e. intermediate

Falsic??

Aphanitic, phaneritic, and porphyritic are terms that indicate _____, respectively. a. Mixed grain, course grained, and fine grained crystal sizes b. formation by fast cooling, slow cooling, and mixed cooling rates c. plutonic, volcanic, and mixed plutonic volcanic orgins d. fine grained, course grained, and mixed grained crystal sizes e. course grained, fine grained, and mixed grained crystal sizes

Fine grained, course grained and mixed grained crystal sizes

A laccolith forms when a sill ____ and causes the overlying rocks to _____. a. becomes a dike / tilt 90 degrees b. ruptures underground / collapse c. breaks the surface / explode d. inflates / bow upwards e. deflates / melt

Inflates / Bow upwards

Plutons originate through _____ activity. a. igneous volcanic b. intrusive volcanic c. extrusive volcanic d. intrusive igneous e. extrusive igneous

Intrusive igneous

Natural glass such as obsidian forms when _____. a. gas escapes through lava b. pegmatite melts, moves to Earth's surface and re-forms c. magma cools too slowly for crystals to form d. magma has a very low silica content e. magma cools too rapidly or crystals to form

Magma cools too rapidly for crystals to form

One example of a vesicular felsic rock is _____. a. pumice b. obsidian c. mica d. granite e. basalt

Pumice

Stoping is the process in which _____. a. dikes are formed due to intense heat in the country rock b. the viscosity of magma changes due to changes in silica content c. rising magma detaches and engulfs pieces of country rock d. pyrooclastic flows are transformed into obsidian e. erosion exposes batholiths

Rising magma detaches and engulfs pieces of country rock

The term pegmatite refers to an igneous rock with a particular _____ rather than a specific _____. a. texture / composition b. composition / texture c. composition / silica content d. silica content / texture

Texture / Composition

Most igneous rocks are classified as either volcanic or plutonic based on their _____. a. size and location b. magnesium content c. size and composition d. texture and composition e. iron content

Texture and composition.

Mafic lava tends to be fluid, whereas felsic lava is much more viscous. True or False

True

Many geologists now think that hot-spot volcanism results from a rising mantle plume. True or False

True

Basalt and gabbro are compositional equivalents, which means that they _____. a. are made up of the same minerals and are the result of explosive igneous activity b. are made up of the same minerals but have different textures c. have the same texture but one is mafic and the other is felsic d. have the same texture but are made up of different minerals e. are booth formed from the same pluton

are made up of the same minerals but have different textures

The process of assimilation _____. a. includes melting and incorporation of inclusions of country rock b. results in additional heating of a magma body c. occurs in all plutons d. separates malfic rock from felsic rock e. includes the inclusion of country rock in an extrusive magma

includes the inclusion of country rock in an extrusive magma

Volcanoes have a cylindrical conduct known as a volcanic _____ that connects a. tube b. pipe c. funnel d. neck e. cord

pipe