because it just is
Quartz
it depends on if it is intrusive or extrusive (intrusive is below the earth and extrusive is at or above the earth) intrusive has a bigger crystal because it takes time to cool down.
If the rocks are igneous then in general:- Coarse = slowly. Fine = fast. However if the rocks are metamorphic or sedimentary then grain size has nothing to do with cooling and indicates other things.
Obsidian is formed from very rapidly cooling lava.
Well, honey, those are crystals we're talking about. Igneous rocks can have different crystal sizes depending on how fast they cool. So, if you see some big crystals in a rock, it probably cooled slowly, and if you see tiny crystals, it cooled quickly. It's like a rock's own little time capsule of its formation process.
Quartz
Extrusive igneous rocks are fine grained due to fast cooling. They cool at a faster rate than most igneous rocks.
Crystal size is largely dependent on the time the magma takes to cool and solidify. Slow cooling equals large crystals. Fast cooling equals small crystals.
it depends on if it is intrusive or extrusive (intrusive is below the earth and extrusive is at or above the earth) intrusive has a bigger crystal because it takes time to cool down.
If the rocks are igneous then in general:- Coarse = slowly. Fine = fast. However if the rocks are metamorphic or sedimentary then grain size has nothing to do with cooling and indicates other things.
Obsidian is formed from very rapidly cooling lava.
Rocks formed by fast cooling magma are typically fine-grained and include rocks like basalt, andesite, and rhyolite. These rocks cool quickly on or near the Earth's surface, resulting in small mineral grains and a smooth texture.
Since you have neglected to describe them or provide pictures, that cannot be determined.
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.
Well, honey, those are crystals we're talking about. Igneous rocks can have different crystal sizes depending on how fast they cool. So, if you see some big crystals in a rock, it probably cooled slowly, and if you see tiny crystals, it cooled quickly. It's like a rock's own little time capsule of its formation process.
The cooling rate of magma/lava determines the crystal size in igneous rocks. Fast cooling results in small crystals or glassy texture (e.g., obsidian), while slow cooling leads to large crystals (e.g., granite). Factors like depth of magma intrusion, presence of water, and pressure can also influence crystal size.
Fast and slow are relative terms. If a heated igneous rock takes 3 hours to cool, is that fast or slow? During their formation, however, magma can solidify very slowly or very quickly. Rocks that have cooled quickly from magma are referred to as extrusive igneous rocks, such as obsidian and scoria. Rocks that have formed from slow cooling magma are called intrusive igneous rocks, such as granite and gabbro. The difference between the two types is in their grain size. Slow cooling magma produces large grained rock, and fast cooling magma produces fine-grained rock.