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 formed from the solidification of molten rock material. There are two basic types. Intrusive igneous rocks crystallize below Earth's surface and the slow cooling that occurs there allows large crystals to form.Examples of intrusive igneous rocks are diorite, gabbro, granite, pegmatite, and peridotite.abbro is a coarse-grained, dark colored, intrusive igneous rock that contains feldspar, pyroxene and sometimes olivine. The specimen shown above is about two inches (five centimeters) across. Obsidian is a dark-colored volcanic glass that forms from the very rapid cooling of molten rock material.