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.
Types of igneous rock textures: 1. Aphanitic: fine-grained, less than 1 mm, grains not seen with unaided eye 2. Phaneritic : âcoarse grainedâ; visible crystals; 1 to 10mm. 1. Felsic: generally the lighter-colored igneous rocks; enriched in silica and aluminum bearing minerals (e.g. quartz and potassium feldspar). 2.