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When lava cools extremely fast it forms volcanic glass, better known as obsidian. This often occurs when lava hits water.
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Some extrusive igneous rocks such as obsidian are glassy because they are what?
They cool to quickly for crystals to form.
Does lava cool quickly and form minerals with small crystals?
Yes. The faster lava cools, the less time crystals have to form. If the lava cools slowly and has a low viscosity, atoms are able to move around more and form larger crystals.
Is an intrusive crystal bigger than an extrusive crystal?
Typically, intrusive crystals are larger than extrusive crystals because intrusive rocks cool slowly beneath the Earth's surface, allowing larger crystals to form, while extrusive rocks cool quickly at the surface, producing smaller crystals.
Why do extrusive rocks have small grains?
The intrusion is insulated by the surrounding rock, letting it cool very slowly and allowing crystals time to grow to larger sizes. In rapidly cooled rocks the grains can be so small that they are almost undetectable as no significant crystal growth happened.
What are the conditions which small and large crystals are likely to form?
Small crystals are likely to form when the solution cools quickly or when there are impurities present that inhibit crystal growth. Large crystals are likely to form when the solution is allowed to cool slowly or when there is a high concentration of solute in the solution.
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
Why do igneous rocks that cool quickly have smooth and shiny textures?
Igneous rocks that cool quickly do not have time to form large crystals. This results in a fine-grained texture that appears smooth and may reflect light in a shiny manner. Examples of these rocks include basalt and obsidian.
When lava cools quickly large crystal form?
No. Small crystals form.
Explain 2 ways Igneous Rocks Form?
Igneous rocks form when magma cools and solidifies either underground (intrusive rocks) or on the Earth's surface (extrusive rocks). Intrusive rocks cool slowly, allowing large crystals to form, while extrusive rocks cool quickly, resulting in tiny crystals or glassy textures.
Can extrusive igneous rocks be both fine grain and course grain?
No only fine grained as they cool quickly when out of the earths mantle so no time for crystals to form.
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.
