Crystal Volcanic Rock Mineral Geology

CHAPTER 4 Crystal Volcanic Rock Mineral Geology

In this chapter we discuss crystal volcanic rock mineral geology.


What type of igneous rock consists of very coarse crystals?

Pegmatite


Which texture listed below would be most unlikely to occur in an extrusive igneous rock?

Phaneritic


Why are lava flows typically finer grained than intrusive igneous rocks?

Because the extrusive magma cools quickly and mineral grains do not have time to grow


Which term describes a texture of igneous rocks that crystallized over a single, long period?

Phaneritic


Which minerals crystallize early in Bowen’s reaction series?

Olivine


What term describes the sizes, shapes, and arrangements of mineral grains in an igneous rock?

Texture


Which of the following paris of igneous rocks exhibit aphanitic texture

Ansesite; Rhyolite


A South America mountain range, which rock forms from volcanic activity there?

Andesite


In a porphyritic volcanic rock, which mineral grains are the last to crystallize?

Matrix or groundmass


What is the dominant feldspar in basalt?

Plagioclase


Why would a plume of solid silicate rock rising slowly from deep in the mantle begin melting as it neared the base of the lithosphere?

Temperatures remain high as lowered pressures decrease melting temperatures.


Which term describes the changing of the composition of magma by incorporating surrounding host rock?

Assimilation


Which of the following rocks has the same mineral composition as andesite?

Diorite


Which of the following rocks are composed mainly of ferromagnesian minerals?

Peridotite


The last minerals to crystallize on Bowen’s Reaction Series result in igneous rocks with a __________ composition.

Felsic


Of those below, which igneous rock or magma has the lowest silica (SiO2) content?

Peridoite


What is the dominant lava erupted from volcanoes on Hawaii and Iceland?

Basalt


What ingeous rock has a pyroclastic texture, meaning it was formed from a glowing avalanche

Welded tuff


Which of the following is a factor that does not affect the generation of magma?

Crystal size


Which volcanic rock is extremely vesicular and glassy?

Pumice


What do pumice and obsidian have in common?

Glassy Texture


A __________ is an open cavity in a volcanic rock that was filled by a gas bubble when the lava was still mainly liquid.

Vesicle


What ultramafic rock is though to be common in Earths mantle but rare in the crust?

Peridotite


Which of the following are used for studying rocks with a polarizing or petrographic microscope?

Thin sections


Which rock would be most likely to contain visible quartz and potassium

Granite


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