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.
Let's review. Igneous rocks are rocks made from the cooling and solidifying of molten rock. There are two categories of igneous rocks. Volcanic rocks are rocks formed when lava cools and solidifies on the earth's surface.Volcanic rocks are also known as 'extrusive igneous rocks' because they form from the 'extrusion,' or eruption, of lava from a volcano.he term 'igneous' comes from the Latin language and is the word for 'fire,' which is a very appropriate name due to the fact that igneous rocks originate from fiery, red-hot magma. We associate magma with volcanoes, yet you don't actually see magma because by definition, magma is located below the surface of the earth.