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What does the color of an igneous rock indicate?

What does the color of an igneous rock indicate?

Colour index, in igneous petrology, the sum of the volume percentages of the coloured, or dark, minerals contained by the rock. Broadly speaking, mineral colour indicates the specific gravity of the mineral; minerals that are lighter in colour are also lighter in weight.

Are igneous rocks classified by color?

Composition and Color Composition influences the color of igneous rocks. Felsic rocks tend to be light in color (white, pink, tan, light brown, light gray). Mafic rocks tend to be dark in color (black, very dark brown, very dark gray, dark green mixed with black).

Which igneous rock is light in color?

Light-colored igneous rocks (pumice, rhyolite & granite) are composed of larger amounts of silica and are said to be felsic (feldspar + silica). Such light colored minerals include quartz and orthoclase (potassium) feldspar.

What does igneous look like?

Answer: Extrusive, or volcanic, igneous rocks look dull and do not sparkle much because they are fine grained. If the magma stays inside the earth and takes thousands of years to cool, it has time to make big crystals.

Why is igneous dark in color?

A rock that has a large amount of ferromagnesian minerals in it will be a dark-colored rock because the ferromagnesian minerals (other than olivine) tend to be dark-colored; an igneous rock that is dark in color is called a mafic rock (“ma-” comes from magnesium, and “fic” from ferric iron).

Why the Colour of igneous rocks is dark?

Why would igneous rocks appear dark in Colour? The color distinction comes from the differences in iron and magnesium content. Iron and, to a lessor extent, magnesium give minerals a darker color. Intermediate igneous rocks tend to have intermediate shades or colors (green, gray, brown).

What color is rock?

Igneous Rock Charts

Texture V Color> Light colored: Pink, white, Gray, Green, Lavender
Minerals > 10 – 30% orthoclase (potassium-feldspar) 10 – 40% quartz 0-33% Na plagioclase 8-15% amphibole and biotite
Composition Felsic (sialic)
Fine = aphanitic Extrusive volcanic Rhyolite
Coarse = phaneritic Intrusive plutonic Granite

What is the color of sedimentary rock?

The colors of sedimentary rocks can have complex origins and in cases are secondary. For the most part the colors of sediment and sedimentary rock fall within two spectra: green-gray to red and olive-gray to black (Figure C70).

What igneous rock is red?

Alkali feldspar granite, some varieties of which are called ‘red granite’, is a felsic igneous rock and a type of granite rich in the mineral potassium feldspar (K-spar). It is a dense rock with a phaneritic texture.

What is a dark-colored igneous rock called?

What kind of rock is pink?

A rock-forming mineral with a pink or pinkish color is almost certainly feldspar.

What are three examples of igneous?

These rocks include: andesite, basalt, dacite, obsidian, pumice, rhyolite, scoria, and tuff.

What are the different colors of igneous rocks?

Igneous rocks are classified based on only 4 colors: mafic, ultramafic, felsic, and intermediate. Below is a table with examples of each color of igneous rock. No quartz or potassium feldspar is found. These are your dark green, brown, red, gray and black igneous rocks.

What is the color index of a rock?

The color index of igneous rocks is a very useful indicator of the types of minerals present in the rock and therefore the specific type of rock. The color index of an igneous rock is a measure of the ratio of dark colored, or mafic, minerals to light colored, or felsic, minerals.

How are the colors of rocks affected by the elements?

Color in rocks is controlled by the color of the minerals in the rock which in turn is controlled by the elements particularly the metals. The elements effect the optical properties of the minerals, which is the absorption of parts of the colors of the spectrum and hence the color we see. The atmosphere scatters blue light and hence looks blue.

What is the Colour Index of a mafic rock?

Learn More in these related Britannica articles: In this regard, the term colour index, which refers to the total percentage of the rock occupied by mafic minerals, is useful. Felsic rocks have a colour index of less than 50, while mafic rocks have a colour index above 50.

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