The Colors Of Granite Depend On The Mineral Grain Size

Of course diorite and andesite have the same mineral content and occur in the same areas.

The colors of granite depend on the mineral grain size.

The specimen above is a typical granite. The difference is grain size and cooling rate during the rock formation process. Slow cooling of diorite results into coarse grain size due to large crystals formation with more ion transport. Quartz is milky white feldspar is white potassium feldspar is pink biotite is black or brown muscovite is yellow and amphibole is green.

But a rapidly cooled volcanic rock with the same composition as the granite could be entirely. Under certain conditions the mineral grains can grow very large. The grain size is coarse enough to allow recognition of the major minerals. On the other hand if the molten rock is abundant in quartz and minerals that make.

The pink grains are orthoclase feldspar and the clear to smoky grains are quartz or muscovite. Grain size can vary greatly from extremely coarse grained rocks with crystals the size of your fist down to glassy material which cooled so quickly that there are no mineral grains at all. The black grains can be biotite or hornblende. Numerous other minerals can be present in granite.

Trace minerals such as mica and amphiboles also affect the color and composition. One objection to the earth being only 6 000 years old as described in the bible is the claim that the coarse grained texture of granites shows they cooled slowly over millions of years. The most common colors of granite are white pink yellow grey and black primarily because of its composition. Coarse grain varieties with mineral grains large enough to see without a magnifying glass are called phaneritic.

Peridotite basalt gabbro diorite rhyolite. Granite and gabbro are examples of. The minerals found in granite are typically light colored and may vary depending on which minerals are prevalent. Ferromagnesium minerals are dark colored.

But color can be misleading when applied to rocks of the same composition but different grain size. The classification of igneous rocks depends on both grain size and silica composition. If the molten rock was abundant in potassium feldspar the granite is more likely to take on a salmon pink color. It is about two inches across.

Not a problem for rapid cooling of plutons. For example a granite consists of lots of quartz and feldspar and is generally light colored.