1. Carbon (C) the Nacre and Its Allotropes

Carbon (identified by a symbol C in the periodic table of elements, Fig. 1.3) is an interesting element; you cannot see (C, pronounced as see) the C all the time, but the existence of the element (C) is almost everywhere. It is in your clothes, in your backpack, in your food, and in your body. It provides the framework for all tissues of plants and animals (rational and irrational). These tissues are built of elements grouped around chains or rings made of carbon atoms. Indeed, most of the structures that make up animals, plants, and microbes are made from three basic classes of molecules: amino acids, carbohydrates, and lipids (often called fatty acids), and all of these materials contain carbon as their backbone [1, 2]. As these molecules are vital for life, metabolic reactions either focus on making these molecules during the construction of cells and tissues, or breaking them down and using them as a source of energy during digestion [3]. As a matter of fact, carbon (C) occurs in nature as the sixth most abundant element in the universe and the 19th element in order of mass in the Earth’s crust.