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In many cases the molten rock at the surface cools too quickly for crystals to form.

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Q: Why don't crystals always form in extrusive rock?
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Why don't crystals always form in extrusive rocks?

In some cases the molten rock cools too quickly for the atoms to arrange themselves into a crystalline structure.


Is diamond an intrusive or extrusive rock?

Intrusive because they have large crystals and the have these because they have cooled down much slower then extrusive due to the heat inside the volcano; meaning the crystals took longer to form.


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 is the extrusive form of granite with extremely small crystals and a red pink or gray color?

Rhyolite


Some extrusive igneous rocks such as obsidian are glassy because they are what?

They cool to quickly for crystals to form.


Is it extrusive rock that can have smooth texture because it is formed from lava that cooled so quickly that large crystals did not have time to form or is it intrusive?

Extrusive Igneous rock cools quickly above ground so it has a smooth texture so there isn't enough time for crystals to form and intrusive igneous rock forms inside a volcano or other underground hot place and takes longer to cool so crystals can form. It is extrusive.


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.


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.


What is extremely rapid cooling of lava in which no crystals form?

Extrusive is when Igneous rock is formed from magma below Earth's surface.


Would you list intrusive rocks under rocks that form above the ground or below?

Intrusive rocks are Igneous rocks that have been formed underground. Igneous rocks are formed by the cooling of lava/magma. Igneous rocks are divided into two categories- intrusive and extrusive. Intrusive is when the magma cools slowly beneath the Earth's surface, which causes large crystals to form. When lava cools above the Earth's surface, it is called extrusive. Extrusive rocks have smaller crystals compared to intrusive, the difference always being noticable.


What do crystals always form?

a mineral


Which igneous rock can be intrusive and extrusive?

A porphyritic igneous rock demonstrates some extrusive characteristics and some intrusive characteristics. The appearance of phenocrysts (larger crystals) in a fine matrix (small crystals) indicates that the magma had time to cool slowly enough underground to form larger crystals before being erupted at or near the surface.