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 also formed when volcanoes erupt. Igneous rocks are formed as the lava cools above ground. The upper 16 km of the Earthâs crust is composed of 95% igneous rock. Intrusive igneous rocks are formed from magma that cools and solidifies underground.These rocks are coarse grained.gneous rocks are formed as the lava cools above ground. The upper 16 km of the Earthâs crust is composed of 95% igneous rock. Intrusive igneous rocks are formed from magma that cools and solidifies underground. These rocks are coarse grained.