A mineral is naturally occurring, inorganic, and has a fixed composition and a repeating internal structure. Rocks are made of minerals… 3.3 Elements are the building materials of minerals…. • Atomic structure c.f. 3.5 3.4 Ionic bonds result from the transfer of an electron… Halite is a perfect example of an ionic solid… Halite c.f. 3.7 3.12 1 • Covalent bonds result from sharing of Diamond and graphite are examples of ‘native’ carbon… electrons…. Elemental carbon, as diamond, is a perfect example of a covalently- bonded material. 3.15 Metallic bonding Structure of minerals • Polymorphs • Minerals with the same composition but different crystalline structures • Examples include diamond and graphite » Phase change = one polymorph changing into another ‘Native’ copper…. Physical Properties of Minerals: Color: • Crystal form Quartz (SiO2) exhibits a variety of colors • External expression of a mineral’s internal structure Figure 3.26 2 Hardness: Cleavage: Mohs scale of hardness Figure 3.22 Figure 3.20 Fluorite, halite, and calcite and muscovite Physical properties all exhibit perfect cleavage of minerals • Fracture • Absence of cleavage when a mineral is broken • Specific Gravity • Weight of a mineral / weight of an equal volume of water • Average value = 2.7 Physical properties Conchoidal fracture of minerals • Other properties • Magnetism • Reaction to hydrochloric acid • Malleability • Double refraction • Taste • Smell • Elasticity Figure 3.23 3 Elemental abundances in continental crust Mineral groups • Silicates • Most important mineral group – Comprise most rock-forming minerals – Very abundant due to large % of silicon and oxygen in Earth’s crust • Silicon-oxygen tetrahedron – Fundamental building block – Four oxygen ions surrounding a much smaller silicon ion c.f. 3.26 Silicate Two Minerals illustrations of the Si–O Silica tetrahedron tetrahedra link to form: Figure 3.27 3.29 Chapter 4 Table 3.2 4.