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Granite has a very similar chemistry to rhyolite. However, granite solidifies & crystallises in intrusions deep beneath the surface where the INSULATED environment results in the granite cooling slowly and therefore, having large crystals.
Rhyolite solidifies at the surface, generally directly from volcanic lava, where it cools very rapidly due to lack of insulation from contact with surface temperature rocks & air. As a result of its rapid cooling, it has very small crystals.
by aidan
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Why do some igneous rocks have big crystals or grains and some igneous rocks have small crystals or grains?
how long they stayed in the volcano; how much time the crystals had to form
Name some rocks which have crystals?
All rocks have crystals, or at least crystalline structures. Sedimentary rocks may not have crystals as such, but the individual grains have internal crystal structures. All magmatic and metamorphic rocks have crystals, though they may be too small to be seen without the aid of a microscope. Only possible exception is Obsidian (volcanic glass) which may be amorphous.
Minerals of extrusive rocks are so small that what is needed for identification?
Extrusive rocks will not always necessarily have small crystals, but they do tend to experience cooler temperatures and as such do often have smaller crystals. When the rock has cooled particularly quickly and the crystals are very small indeed, a microscope must be used to examine them. For the most part, however, a hand lens will be sufficient.
What is an igneous rock with small crystals?
If you're not looking for anything specific, any extrusive igneous rock will have smaller crystals, if any at all. This is because they cool quickly on the surface, leaving little time for crystals to form/grow.
What type of crystal are formed from in extrusive igneous rocks?
Small crystals, invisible without magnification.
Do igneous rocks have small crystals large crystals or no crystals?
It depends on the type of igneous rock. Intrusive igneous rocks such as granite have large crystals, extrusive igneous rocks may have small crystals as in basalt or no crystals as in pumice.
What are Igneous rocks that have large crystals and small crystals?
Such rocks are called porphyritic.
Where would you expect to find an igneous rock with small crystals?
you would find igneous rocks with small crystals at the bottom of the volcano, this is because when the rocks crack. It brakes apart into igneous rocks
Why do some igneous rocks have big crystals or grains and some igneous rocks have small crystals or grains?
how long they stayed in the volcano; how much time the crystals had to form
Do extrusive rocks cool quickly?
Extrusive rocks do cool quickly because either the crystals in the rock are very small or there are no crystals at all.
Why do some igneous rocks have larger crystals but other igneous rocks have crystals so small they have to be seen with a microscope?
Crystal size in igneous rock is dependent on the amount of time spent in cooling from magma or lava. More time means larger crystals. Rocks that have small crystals cooled quickly, so the minerals didn't have time to rearrange and form large crystals before the rock solidified. These small-crystalled rocks are described as aphanitic. Other rocks cooled slowly, so the minerals had time to rearrange and form large crystals before solidifying. These rocks are considered phaneritic. Some rocks cool slowly for a while, and then experience rapid cooling (such as magma that cools slowly inside a volcano, and then cools rapidly when the volcano erupts). Such rocks have large crystals surrounded by tiny crystals. Rocks that form this way are described as porphyritic.
Some WHAT igneous rocks have individual mineral crystals that are too small to be seen without magnification?
Some extrusive igneous rocks have individual mineral crystals that are too small to be seen without magnification.
Do you think extrusive or intrusive igneous rocks are likely to have larger crystals?
If a rock has large crystals, it is an intrusive rock. Intrusive rocks form underneath the Earth's surface. Magma cools slowly so it has time to form large crystals. An example is granite, where you can see the crystals with your naked eye. Rocks that have small crystals are extrusive rocks. Extrusive rocks are ones that form from lava (blasted out of a volcano) so they cool very quickly, not allowing large crystals to form. An example is obsidian, where you cannot visibly see the small crystals; it just looks like one black, glassy rock.
Name some rocks which have crystals?
All rocks have crystals, or at least crystalline structures. Sedimentary rocks may not have crystals as such, but the individual grains have internal crystal structures. All magmatic and metamorphic rocks have crystals, though they may be too small to be seen without the aid of a microscope. Only possible exception is Obsidian (volcanic glass) which may be amorphous.
Do igneous rocks have large crystals?
Yes, they can. Extrusive igneous rocks, which form outside the Earth's surface, often contain small or no crystals, because they cool quickly and the particles in the lava do not have much time to arrange themselves. Intrusive rocks, which form inside the Earth, generally have large crystals because they cool slowly. Granite is an example of an igneous rock with large crystals.
Why do some rocks have crystal?
it all depends on the rate of cooling and crystallisation and the type of rock
What is the difference in appearance between igneous rocks that have cooled slowly and igneous rocks that have cooled quickly?
Igneous rocks that cooled slowly are intrusive. Igneous rocks that cooled quickly are extrusive. Intrusive rocks form larger crystals, because the crystals have a longer time to grow. Extrusive rocks have small to no crystals, because they had little or no time to grow/form.
