Densities of Granitic and Basaltic Crustal Rocks Found Using a Quadruple Beam Ba

Question

Densities of Granitic and Basaltic Crustal Rocks Found Using a Quadruple Beam Balance Do the densities you measured for the crustal rocks granite and basalt compare well with the values presented on page 2-16? We assume that mantle rocks have a composition similar to the rock peridotite, which is largely made up of the minerals olivine and pyroxene and is denser than crustal rocks (up to 5.7g/cm^3). Laboratory experiments indicate that peridotite has physical properties that account for the mantle's density and observed rates of seismic wave transmissions Also, samples from the field show peridotites below crustal rocks in areas of deformation where rocks have been uplifted and exposed at the surface Peridotite inclusions are also found in kimberlite pipes, cone-shaped bodies of rock where magma has been volcanically emplaced into pre-existing rocks Kimberlite deposits contain certain minerals (one of which is diamond), which can only form under the high pressure and temperature conditions found between 100 - 300 km depth. The inclusion, of peridotite in the kimberlite are thought to represent piece of the mantle brought to the surface during eruption. A final piece of evidence used to determine the mantle's composition comes from stony meteorites, since they are thought to be remnants of material left over from the formation of the solar system, and they have peridotitic composition. There is a specimen of peridotite (the greenish rock, #44) at your station, Its density is 3.12 g/cm^3.

Explanation / Answer

The calculated density of granite = 2.41 g/cm^3

Calculated density of basalt = 2.89 g/cm^3

Standard density of granite = 2.60 - 2.80 g/cm^3

Standard density of Basalt(given in books) =2.80 -3.0 g/cm^3

Yes, the density measured from the rocks(calculated density) is comparable to that given in the books.

However, the measured density of granite is found to be slightly lower than the standard value.

It can be due to substandard granite taken for experiment or experimental errors .

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