MINERALS2 - 9 Minerals I- Introduction So far we have been...

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9 Minerals I- Introduction So far we have been studying some large scale features such as the composition and structure of the Earth and its plates. These features can be understood by studying the building blocks of the earth's crust and mantle: the rocks. So what is a rock? A rock is an aggregate of minerals formed by natural processes. This leads us to ask: what is a mineral? A mineral is a naturally occurring, inorganic solid, that has a specific chemical composition, and a definite internal structure. It is clear from this definition that minerals are not the smallest building blocks of matter, but are actually chemical compounds . Therefore, before we examine carefully the various parts of the definition of a mineral and figure out which "substances" qualify for this definition, we must learn some basic chemical principles. All minerals have a certain chemical composition, and are thus made of one or more elements . An element is a substance in which all atoms have the same nuclear charge. As such, each element has unique physical and chemical properties, defined by the structure of its atoms . An atom , the building block of the element, is the smallest part of matter that still retains the characteristics of this element. Accordingly, elements, which are aggregates of atoms of the same type, combine with each other to form compounds , some of which qualify for the definition of a mineral. In order to understand how compounds (and hence minerals) form by the combination of elements (a process known as bonding ), we must examine the internal structure of the atom. II- The atomic structure Atoms: The atom consists of neutral neutrons and positively charged protons (which form a dense nucleus) surrounded by negatively charged electrons . In each atom, electrons revolve around the nucleus in orbits (or shells ). Each atom is electrically neutral, so it must have a number of electrons equal to the number of protons in its nucleus. Atomic number Is the number of protons (or electrons) in one atom of the element concerned. Mass number Is the sum of number of protons and neutrons in the atom of the element of ineterst.
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10 Geol 111 El-Shazly, A. K., 2000. Isotopes Isotopes of an element are atoms of the same element that have the same atomic number (of course!) but a different mass number. This is simply because of a difference in the number of neutrons in each isotope. Example: Oxygen has three isotopes: 16 O, 17 O, and 18 O. All three have the same number of protons and electrons (8), but a different number of neutrons. Shells or energy levels: Different shells with different energies occur at different distances from the nucleus. These shells, also known as energy levels , are labelled K, L, M and N, with the K shell being that one closest to the nucleus, and is characterized by the lowest energy (Fig. 1). An electron revolving around the nucleus in the K shell will have a lower energy
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MINERALS2 - 9 Minerals I- Introduction So far we have been...

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