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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.
What does it mean if an igneous rock has large crystals?
It has cooled slowly under the Earth e.g. in magma chamber. This is why granite has large crystals but extruded/erupted lava only has microscopic crystals since the latter has cooled very quickly.
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.
Must all rocks form crystals?
All rock does not contain mineral crystals. Obsidian, or volcanic glass, in particular is a rock that has cooled so quickly from lava that mineral crystals were not able to form.
How do halite crystals form in a desert on a dry lake floor?
Halite crystals form due to evaporation of the water in which it is dissolved. When this occurs, the sodium and chloride ions - which, when combined, make salt - move closer together and form the salt crystals. The halite crystal would form very quickly under these conditions because the evaporation would be quicker, due to the heat. Also, would result in smaller crystals, whereas slow evaporation will result in larger crystals.
Andesite has small crystals because?
Andesite has small crystals because it formed from lava that cooled relatively quickly at the Earth's surface, preventing larger crystals from growing. Rapid cooling does not allow enough time for the minerals to crystallize fully, resulting in smaller crystal sizes.
What does lava that cools quickly form?
fast cooling lava -small crystals or no crystals
What lava that cools quickly form?
fast cooling lava -small crystals or no crystals
As the rate of cooling of igneous rocks increases the size of the crystals that form?
The size of crystals decreases as the cooling increases. This is called an inverse relationship.
Why do rocks formed from lava have small crystals?
That's because of the cooling speed. When a magma or a lava cools, it forms crystals. The longer these crystals have the time to form, the larger they will be. However, at the surface, the lava cools relatively fast (at least, compared to magma that stays inside the earth). The crystals in the rock that forms that way don't have a lot of time to form, so don't grow big.
Obsidian pumice and scoria lack crystals because?
Obsidian lacks crystals because it is a type of volcanic glass that cools too quickly for mineral crystals to form. Pumice and scoria lack crystals due to their porous nature and high gas content, preventing the growth of crystalline structures during cooling.
How does the crystal sizes of igneous rocks indicate the rate of cooling and whether the rock is extrusive or intrusive?
Generally, large crystals represent slow cooling rates and small crystals represent fast cooling rates. Crystals need time to form and since extrusive rocks cool very quickly, they have very tiny crystals and some don't even have crystals because the rate of cooling was so fast that crystals didn't have time to nucleate. On the other hand, intrusive rocks cool rather slowly allowing crystals to grow.
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.
How does the cooling rte of rocks affect the crystal size?
If rock cools quickly it does not have time to form large crystals and so it forms small ones. At slower cooling rates there is time to form larger crystals.
What are Igneous rocks that have large crystals and small crystals?
Igneous rocks with large crystals are called intrusive rocks, formed from magma cooling slowly beneath the Earth's surface, allowing for large crystals to form. Igneous rocks with small crystals are called extrusive rocks, formed from lava cooling quickly on the Earth's surface, resulting in small crystals due to rapid cooling.
What is the relationship between cooling time igneous rocks and the size of its crystals?
Plutonic rocks are intrusive (they solidify before they reach the surface) and have larger crystals because the crystals have had a longer time to accumulate in the heat under the surface. Volcanic rocks are extrusive (they solidify on or near the surface) and have smaller crystals because the element has less time to accumulate when they cool quickly.
How is the size of mineral crystals in igneous rock related to the rate at which they cool?
When igneous rocks cool quickly, they have small crystals and have a texture that may be described as aphanitic. When igneous rocks cool slowly, they have much larger crystals and have a texture that may be described as phaneritic or pegmatitic.
