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.
Granite is a good example of an intrusive igneous rock. Extrusive rocks cool above the earth's surface and crystallize very quickly, as a result are finer grained. Extrusive rocks are released from the earth in the form of volcanic eruptions, which occur both on the continents and on the ocean floor.ntrusive igneous rocks is formed from magma that cools, solidifies, crystallizes, and hardens slowly within the earth's crust, and this makes its crystals large.