1 It is proven that a cup of hot coffee can help uplift your senses and refresh you. This quality of coffee can be attributed to the presence of caffeine, which is a central nervous stimulant.  Caffeine is basically a bitter white crystalline alkaloid.
1 Igneous rocks that form too quickly for crystals to form have what is called a glassy texture. 2  Obsidian is the only glassy igneous rock, and can be identified by its dark color. 3  This looks like dark black glass. An example of an intrusive rock is granite. 2  When magma is above the earth's crust, it is known as lava. 3  Extrusive rocks form through very fast cooling of lava above the Earth's surface. 4  Extrusive rocks have very small, almost microscopic crystals.
It can also explode violently, dispersing magma into the air that falls back to the surface as ash and tuffs. Compared to intrusive rock, this type of igneous rock cools and crystallizes at a much faster rate due to it being exposed to air or water, which results in it being fine-grained. 1  How igneous rocks are formed. Credit: Wikipedia Commons/Jasmin Ros. 2  Basalt rock, a common form of igneous rock.