However, the issue of granite cooling does not stop there. Critics of the biblical age of the earth argue that the texture of granite means it must have cooled very slowly. Granite has a crystalline texture of interlocking mineral grains ranging from 1–5 mm (Figure 3).
Sceptics allege that if the magma had cooled quickly, the texture would have been a fine-grained lava-like rock or even a volcanic glass. However, this objection is based on the false idea that grain size depends solely on cooling rate.
Granitic dykes and pegmatites are well-known examples of granitic rocks that formed when cooling was more rapid than the cooling of a pluton. Also, large fine-grained rhyolite bodies show that coarse-grained texture does not necessarily form when cooling is slow within them.
If cooling rate was the only factor affecting grain size, the inside of such a large volume of magma would cool more slowly and produce a coarser-grained texture. What are some of the factors, other than cooling rate, that affect grain size?
If the magma cools quickly, the crystals do not have much time to form, so they are very small. If the magma cools slowly, then the crystals have enough time to grow and become large. Some granites contain minerals which are up to one meter (3 ft) across!
Granite and granodiorite are intrusive igneous rocks that slowly cool deep underground in magma chambers called plutons. This slow cooling process allows easily visible crystals to form.
As magma cools it undergoes reactions that form minerals. The rate of cooling is very important. If the magma cools slowly then the reactions proceed for a longer period of time and the resulting mineral crystals (grains) become large.
Looks Good! Correct: Granite is an example of an igneous rock that formed by slow cooling 30-40 km below the earth's surface. Slow cooling in this specimen from New Mexico produced large crystals, visible to the naked eye.
coarse-grainedGranite is a coarse-grained rock composed of aluminosilicate minerals that crystallizes slowly and at much higher temperatures than basalt.
Granite (/ˈɡrænət/) is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies underground.
Intrusive Igneous RocksIntrusive Igneous Rocks Deep in the crust, magma cools slowly. Slow cooling gives crystals a chance to grow. Intrusive igneous rocks have relatively large crystals that are easy to see. Intrusive igneous rocks are also called plutonic.
Slow cooling allows time for large crystals to form, so intrusive igneous rocks have visible crystals. Granite is the most common intrusive igneous rock (see Figure below for an example). Igneous rocks make up most of the rocks on Earth.
Igneous rocks contain randomly arranged interlocking crystals. The size of the crystals depends on how quickly the molten magma solidified: magma that cools slowly will form an igneous rock with large crystals. lava that cools quickly will form an igneous rock with small crystals.
The texture of an igneous rock (fine-grained vs coarse-grained) is dependent on the rate of cooling of the melt: slow cooling allows large crystals to form, fast cooling yields small crystals.
If magma cools quickly, for example when basalt lava erupts from a volcano, then many crystals form very quickly, and the resulting rock is fine-grained, with crystals usually less than 1mm in size. If magma is trapped underground in an igneous intrusion, it cools slowly because it is insulated by the surrounding rock.
Phaneritic (phaner = visible) textures are typical of intrusive igneous rocks, these rocks crystallized slowly below Earth's surface. As magma cools slowly the minerals have time to grow and form large crystals.
Igneous rocks from cooling magma . Granite is an igneous rock formed from magma that cooled slowly underground. As the magma slowly cools, large mineral crystals form.
Design Report Design a Thermos It’s time to complete your Design Report. Save the lab to your computer with the correct unit number, lab name, and you … r name at the end of the file name (e.g., U2_ Lab_DesignAThermos_Alice_Jones.doc). Problem and Constraints 1.