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Earth Science, 12e Minerals: Building Blocks of Rocks Chapter 2

Minerals: the building blocks of rocks Definition of a mineral • • • • •

Natural Inorganic Solid Possess an orderly internal structure of atoms Have a definite chemical composition

Mineraloid – lacks an orderly internal structure

Composition and structure of minerals Elements • Basic building blocks of minerals • Over 100 are known

Atoms • Smallest particles of matter • Have all the characteristics of an element

Periodic Table of the Elements

Figure 2.4

How atoms are constructed Nucleus – central part of an atom that contains • Protons – positive electrical charges • Neutrons – neutral electrical charges

Energy levels, or shells • Surround nucleus • Contain electrons – negative electrical charges

Simplified view of the atom

Figure 2.5

How atoms are constructed Atomic number is the number of protons in an atom’s nucleus Bonding of atoms • Forms a compound with two or more elements • Ions are atoms that gain or lose electrons

Isotopes • Have varying number of neutrons

How atoms are constructed Isotopes • Have different mass numbers – the sum of the neutrons plus protons • Many isotopes are radioactive and emit energy and particles

Minerals Physical properties of minerals • • • • • •

Habit Luster Color Streak Hardness Cleavage

The mineral quartz often exhibits good crystal shape

Figure 2.21

Pyrite (fool’s gold) displays metallic luster

Figure 2.11

Mohs scale of hardness Figure 2.13

Three examples of cleavage – halite, calcite, and fluorite

Figure 2.15 B

Minerals Physical properties of minerals • Fracture • Specific gravity • Other properties • • • •

Taste Smell Elasticity Malleability

Conchoidal fracture

Figure 2.16

Minerals Physical properties of minerals • Other properties • • • •

Feel Magnetism Double refraction Reaction to hydrochloric acid

Minerals A few dozen minerals are called the rockforming minerals • The eight elements that compose most rockforming minerals are oxygen (O), silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg) • Most abundant atoms in Earth’s crust are oxygen (46.6% by weight) and silicon (27.7% by weight)

Composition of continental crust

Figure 2.19

Minerals Mineral groups • Rock-forming silicates • Most common mineral group • Contain the silicon-oxygen tetrahedron (molecule) • Four oxygen atoms surrounding a much smaller silicon atom • Combines with other atoms to form the various silicate structures

The silicate (SiO4 molecule

Figure 2.20

4– )

Minerals Mineral groups • Rock-forming silicates • Groups based on tetrahedral arrangement • Olivine – independent tetrahedra • Pyroxene group – tetrahedra are arranged in chains • Amphibole group – tetrahedra are arranged in double chains

Hornblende – a member of the amphibole group

Figure 2.21

Minerals Mineral groups • Rock-forming silicates • Groups based on tetrahedral arrangement • Micas – tetrahedra are arranged in sheets • Two types of mica are biotite (dark) and muscovite (light) • Feldspars – Three-dimensional network of tetrahedra

Minerals Mineral groups • Rock-forming silicates • Groups based on tetrahedral arrangement • Feldspars • Two types of feldspar are Orthoclase and Plagioclase • Quartz – three-dimensional network of tetrahedra

Potassium feldspar

Figure 2.21

Minerals Mineral groups • Rock-forming silicates • Feldspars are the most plentiful mineral group • Crystallize from molten material

• Nonsilicate minerals • Major groups • Oxides • Sulfides

Minerals Mineral groups • Nonsilicate minerals • Major groups • Sulfates • Carbonates • “Native” elements

Common nonsilicate mineral groups

Table 2.1

Minerals Mineral groups • Nonsilicate minerals • Carbonates • A major rock-forming group • Found in the rocks limestone and marble • Halite and gypsum are found in sedimentary rocks • Many have economic value

Minerals Mineral resources • Reserves are already identified deposits • Ores are useful metallic minerals that can be mined at a profit • Economic factors may change and influence a resource

An underground halite (salt) mine

Figure 2.22