What is the difference in ultramafic rocks and mafic rocks?

Answer 1

Ultramafic rocks like peridotite and dunite, are igneous rocks that have a very low silica content and very high levels of iron and magnesium. They are therefore more dense than most igneous rock and are found at great depth but appearing on the surface due to volcanic eruption.

Answer 2

Ultramafic rock forms when rock of a very low silica content, even lower than that of mafic rock, solidifies. Simply by its composition, most of Earth's mass is ultramafic rock. Because of its high density, though, nearly all of the ultramafic rock is in the mantle and little of it is present in the crust. There are several possible reasons ultramafic rock may be found at the surface:

1. Ancient lava: During the Precambrian time, when Earth's interior was hotter than it is now, some volcanoes would erupt ultramafic lava.
2. Fractional crystallization: When magma cools underground underground the more mafic components often crystallize first as they have higher melting temperatures than more felsic material. In some mafic intrusions, ultramafic minerals may crystallize and sink to the bottom. Uplift and erosion can then expose the rock after it has cooled.
3. Mantle xenoliths: Sometimes magma will break off and carry away fragments of the surrounding rock. Such rock fragments are called xenoliths. Fragments of the ultramafic rock peridotite have been found in basalt and scoria.

Answer 3

Ultramafic rocks have higher concentrations of magnesium and iron compared to mafic rocks. Ultramafic rocks also have a lower silica content and typically form from the mantle. Mafic rocks have lower levels of magnesium and iron, with higher silica content, and are commonly found in the oceanic crust.

Answer 4

Ultramafic rocks are denser than mafic rocks, and contain less silica and more iron and magnesium. They have a higher melting point as well.

Answer 5

Olivine rocks, (mesospheric rocks).

Answer 6

Yes. The mantle is ultramafic.