Igneous Rocks
Igneous rocks are rocks that were formed from magma or lava after it cooled. They naturally are the strongest of the three types; this is because they are the only rock type to melt, so the atoms are able to create stronger bonds with each other. Obviously, since they come from magma and lava, they require extreme heat to be able to form. Any rock type has the ability to become magma or lava, as long they are exposed to a climate or environment of great heat.
Most people believe that lava and magma are names that can be universally used to describe molten rock, but, scientifically, lava is molten rock that is on the surface of the Earth while magma is molten rock that is still below the surface. But the differences don't stop there, they also both form different types of igneous rocks. Lava forms extrusive igneous rock, a more fine-grained type of this type of rock, while magma turns into intrusive igneous, a rough-grained type of igneous rock. There is a third type of igneous as well, which is slightly more confusing.
Most people believe that lava and magma are names that can be universally used to describe molten rock, but, scientifically, lava is molten rock that is on the surface of the Earth while magma is molten rock that is still below the surface. But the differences don't stop there, they also both form different types of igneous rocks. Lava forms extrusive igneous rock, a more fine-grained type of this type of rock, while magma turns into intrusive igneous, a rough-grained type of igneous rock. There is a third type of igneous as well, which is slightly more confusing.
Extrusive Rock
Extrusive, sometimes referred to as just volcanic, is likely to be more noticeable for having the stone, Obsidian, classified under its category. This stone is popular for it's pretty glass-like look, or in older times it's ability to hold it's own as an arrow head. But, just how does this stone get it's beautiful appearance and sturdy composition? Picture a volcano in the process of erupting, spewing lava all over the land bellow. The lava has been only magma up to this point, not exposed to the cold surface air, and quickly hardens around the spectacular exploding sight. The quick cooling can create a small crystalline structure within the newly formed rock or if the rock were to cool rapidly enough, it could even create an amorphous glass. Obsidian is an example amorphous glass.
As alluded to in the volcano example earlier, magma (that's soon to be lava) can come to the surface through all sorts of cracks and crevices in the Earth. Some of these gaps can include volcanoes (shield volcanoes, stratovolcanoes, etc.), continental rifts, or cinder and spatter cones. There are even different types of lava, ʻAʻā and Pāhoehoe are some of these types. ʻAʻā is a basaltic lava that has chunks of partially molten stone fragments protruding its surface that are called called clinkers. Pāhoehoe is a basaltic lava that has a ropy surface that might be described as somewhat unusual in appearance.
Intrusive Rock
Intrusive, sometimes referred to as plutonic, is less likely to be known but is still easily identifiable with the rock, pumice. If your into beauty treatments or spas you just might have heard about or even used pumice before without knowing! The rock has been shown to scratch off and easily remove dead skin cells, as well as to help rejuvenate dry skin. It can remove the skin, because as stated earlier, most intrusive igneous rock are coarse-grained and rough. The roughness is created by pocket holes or gaps within the magma as it slowly cooled. It gives it a scratchy texture that is able to scratch the dead skin off while leaving behind natural minerals onto the freshly exposed skin.
The slow cooling of an intrusive igneous rock, because it is beneath the Earth and always surrounded by a form of heat, allows the rock to be created with larger crystals. In most cases the crystals can be seen without having to use any tools. This means that intrusive igneous rocks vary from being holey to having large crystals scattered throughout them. The depth at which an intrusive igneous rock is formed can also farther determine what type of intrusive igneous rock that a rock is. Rocks formed near the bottom or mid-level of the crust are called abyssal. While rocks that are formed near the surface of the Earth are called hypabyssal (hypabyssal has special rules to it).
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Hypabyssal
Hypabyssal is classified as an intrusive igneous rock, although technically it is right smack in the middle of both extrusive and intrusive. It is considered to be middle-grained and, like I said, formed fairly close to the surface of the Earth. It is sometimes referred to as subvolcanic rock rather than hypabbysal. It has a porphritic texture between intrusive and extrusive rocks. Basically its size of its crystals tend to vary more than intrusive and extrusive.