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.
Igneous rocks are created when magma (molten rock under the Earthâs crust) cools and becomes solid. Magma loses heat when it moves upwards at weak spots, such as cracks, in the crust. Extrusive igneous rocks form when magma reaches the surface and cools quickly.Fast cooling produces fine-grained rocks.his pink granite shows grains of pink feldspar, white quartz, and black mica. It is formed by slow cooling of molten rock deep in the Earth. Porphyrite (also called microdiorite) is a grey or dark grey intrusive igneous rock.