Igneous rocks quiz

Both of the above

Igneous rocks are named by what observations?

At divergent plate boundaries

Decompression melting occurs where in the Earth?

Gabbro and basalt

Which two igneous rocks make up the oceanic crust?

Phaneritic

Igneous rocks in which you can see the individual mineral grains are called coarse-grained; the technical word is:

“Volatiles”, such as water

“Flux” melting in the mantle is due to the addition of:

Calcium version

In Bowen’s Reaction Series, which version of plagioclase feldspar crystallizes at higher temperatures?

Silica content

Granite, diorite, and gabbro differ in composition due to differences in:

False

Rhyolite is significantly more abundant than granite

False

Basalt is the aphanitic counterpart to diorite

True

Diorite and andesite are composed of similar amounts of feldspars and ferromagnesian minerals

True

Lava is magma on the Earth’s surface

False

The geothermal gradient is the rate at which pressure increases with increasing depth beneath the surface

True

Mafic igneous rocks are silica-poor

True

A mineral’s melting point generally increases with increasing pressure

True

Partial melting of the lower continental crust produces a silicic magma that solidifies into granite or rhyolite

False

An ultramafic rock is composed almost entirely of quartz

True

Pegmatites are extremely coarse-grained igneous rocks

Andesite and diorite

Mineralogically and chemically equivalent rocks are ___ and ___

Peridotite

_, a coarse-grained rock composed of pyroxene and olivine, is the most abundant ultramafic rock

Mantle

Basaltic magma is the result of partial melting of ultramafic rock in the _

Divergent plate boundaries

Most basalt and gabbro on the ocean floor are created at mid-oceanic ridges, which are also:

Lower continental crust

To explain large volumes of granite plutons, partial melting of the _ must take place

More felsic

Partial melting of a rock creates a magma that is _ than the original rock

Addition of water from the subducting plate

Mantle material in a subduction zone partially melts due to:

Convergent boundaries and magmatic underplating

Granitic magmas are associated with:

Different rates of cooling and crystallization

The difference in texture between intrusive and extrusive rocks is primarily due to:

Porphyritic

An igneous rock with large crystals in a fine-grained groundmass is called:

50

Mafic rocks contain about ____% silica

65

Felsic rocks contain about ____% silica