The size of crystals in igneous rocks extrusive is affected by several factors, including the rate of cooling, the temperature of the magma, the composition of the magma, and the presence of volatiles. The rate of cooling determines how much time the crystals have to grow. The temperature of the magma determines the amount of energy available for crystal growth. The composition of the magma determines the types of minerals that can form. The presence of volatiles can inhibit crystal growth.
Crystal Size: The Secret Ingredients of Magma’s Magic
Imagine you’re cooking a pot of soup. As it cools, you might notice crystals or sugar forming at the bottom. That’s what happens to magma too, folks! When magma cools, it forms crystals. And just like in your soup, the size of these crystals depends on a few secret ingredients:
Cooling Rate:
Think of magma as a hot, gooey soup. When you pour it into a cold bowl (the Earth’s surface), it starts to cool down. The faster it cools, the smaller the crystals will be. It’s like when you add sugar to a hot cup of tea and stir it quickly – you get a bunch of tiny crystals.
Viscosity:
Picture magma as a thick, sticky liquid. The more viscous it is, the more it resists flow. So, if the magma is extra sticky, it takes longer for crystals to form and grow. Think of it as trying to stir sugar into a thick pancake batter – it’s a struggle!
Nucleation and Growth Kinetics:
These are fancy terms for how crystals start and grow. Nucleation is when tiny crystal seeds form, and growth kinetics is how fast they grow. If the conditions are just right (think Goldilocks and her porridge), you’ll get big, beautiful crystals.
Dive into the World of Extrusive Igneous Rocks: Grain Size Unveiled
Picture this: you’re exploring a fiery volcanic landscape, lava bubbling and flowing all around. As these molten rivers cool on Earth’s surface, they transform into what geologists call extrusive igneous rocks. But here’s where it gets interesting, my friend! These rocks come in different grain sizes, like snowflakes on a winter’s day. Let’s dive into the different categories and see what makes each one unique.
Grain Size Categories: A Tale of Three Textures
1. Aphanitic Rocks: The Ultra-Fine Grain Whispers
Imagine a rock so tiny-grained, it’s like a gentle whisper to the touch. That’s an aphanitic rock, my friends. Its microscopic grains make it look almost like a smooth, velvety surface.
2. Aphanitic-Porphyritic Rocks: A Clash of Crystal Sizes
Now, let’s add some drama to the mix. Aphanitic-porphyritic rocks are basically a blend of the fine-grained whispers and some larger, more noticeable crystals. It’s like the cool kids at a party, with their fancy crystals standing out from the crowd.
3. Porphyritic Rocks: The Crystal Kings
Meet the grand rock stars of the grain size world: porphyritic rocks. These bad boys flaunt large, conspicuous crystals that demand attention. It’s the rock equivalent of a diamond-studded tiara, with crystals shining bright like the stars above.
What Dictates Grain Size? The Crystal-Control Chronicles
So, what makes these rocks develop such different grain sizes? It all comes down to the crystallization process. Think of it as a race between the cooling lava and the minerals forming within it. If the lava cools too quickly, the minerals don’t have time to grow big, resulting in small crystals (aphanitic) or even no visible crystals (glassy). If the lava chills out a bit slower, the minerals have more time to party and grow larger, creating porphyritic rocks.
Geological Stage-Setters: Where You’ll Find These Rocky Beauties
Extrusive igneous rocks aren’t shy about showing off. You’ll often find them strutting their stuff around volcanoes, lava flows, and even under the waves at mid-ocean ridges and oceanic plateaus. They’re the rock stars of the fiery underworld, adding a splash of color and character to our planet’s surface.
Extrusive Igneous Rocks: The Fast and Furious Story of Lava’s Legacy
Buckle up, folks! We’re about to take a thrilling ride into the world of extrusive igneous rocks, rocks that formed from lava that cooled rapidly on Earth’s surface. Get ready for a tale of fire and fury, where molten rock transforms into solid wonders.
Lava: The Parent of Extrusive Rocks
Lava, the fiery liquid rock that spews from volcanoes, is the raw material for extrusive igneous rocks. As lava cools, it loses its molten state, and minerals start to form and crystallize. The rate at which lava cools plays a crucial role in determining the size of these crystals and the texture of the rock.
Speed Matters: Cooling Rates and Crystal Size
Imagine a pot of hot soup. If you let it cool slowly on the counter, the crystals in the soup will have time to grow large and distinct. But if you stick the pot in the freezer, the crystals will form rapidly and be much smaller. The same principle applies to lava. Rapid cooling rates in extrusive igneous rocks result in tiny crystals that are often invisible to the naked eye, creating a fine-grained texture known as aphanitic.
Grain Size: A Tale of Three Categories
Extrusive igneous rocks come in three main grain size categories:
- Aphanatic: Crystals are so small they’re invisible to the naked eye.
- Aphanatic-porphyritic: A mix of fine-grained crystals with larger, visible crystals called phenocrysts.
- Porphyritic: Large, clearly visible phenocrysts in a fine-grained groundmass.
Diagnostic Minerals: The Clues to a Rock’s Identity
Just like fingerprints, diagnostic minerals can help us identify specific extrusive igneous rock types. Plagioclase feldspar, for example, is common in basalt, while quartz and potassium feldspar are found in rhyolite. By studying the mineral composition, geologists can determine the rock’s chemical composition and the type of magma from which it formed.
Geologic Settings
Where Do Extrusive Igneous Rocks Hang Out?
Extrusive igneous rocks, the cool kids of the rock world, are formed when lava gets its groove on and chills out on the Earth’s surface. These rocks are like the hardened versions of the hot stuff that erupts from volcanoes. Think of them as the rockin’ aftermath of volcanic eruptions.
You’ll find these extrusive igneous rockstars in some pretty rad geological settings:
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Volcanoes: These fiery mountains are the ultimate party spots for extrusive rocks. When magma (molten rock) erupts, it flows out and cools to form new rock layers.
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Lava Flows: These are like the freeways of extrusive rocks. Lava oozes out of volcanoes and creates these rockin’ ribbons as it cools on the Earth’s surface.
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Mid-Ocean Ridges: These are underwater mountain ranges where new oceanic crust is formed. Magma rises from the mantle (the Earth’s gooey interior) and erupts, forming extrusive rocks that create new ocean floor.
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Oceanic Plateaus: These are giant, flat-topped mountains that rise above the ocean floor. They’re formed when massive amounts of lava erupt from the Earth’s mantle and cool on the ocean floor, creating a huge plateau of extrusive igneous rock.
Well, there you have it, folks! We took a dive into the fascinating world of crystals in igneous rocks that formed from rapidly cooled lava. From glassy to porphyritic, each type is a testament to the power of nature’s processes. Remember, the next time you admire a beautiful rock, take a moment to appreciate the incredible journey it went through to form. Thanks for reading, and don’t forget to drop by again for more earth science adventures!