Chapter 2: Minerals: the Building Blocks of Rocks Tarbuck, Lutgens, Tsujita, Hicock, Earth: An Introduction to Physical Geology 3Ce Chapter 2: Minerals: the Building Blocks of Rocks Copyright © 2012 Pearson Canada Inc.

Minerals: The Building Blocks of Rocks Definition of a mineral: Naturally occurring Inorganic Solid Ordered internal molecular structure Definite chemical composition Definition of a rock: A solid mass of minerals Copyright © 2012 Pearson Canada Inc.

The Composition of Minerals Elements Basic building blocks of minerals 113 are known now (90 naturally occurring) Atoms Smallest particles of matter Retains all the characteristics of an element Copyright © 2012 Pearson Canada Inc.

The Composition of Minerals Atomic structure Central region called the nucleus Consists of protons (positive charges) and neutrons (no electrical charges) Electrons Negatively charged particles that surround the nucleus Located in discrete energy levels called shells Copyright © 2012 Pearson Canada Inc.

The Composition of Minerals Atomic structure Atomic number – number of protons in the atom Atomic weight – approximately the total number of protons and neutrons in the nucleus Valence electrons – outer most electrons in the shell Copyright © 2012 Pearson Canada Inc.

The Composition of Minerals Bonding Chemical bonds – strong attractive force forms compounds Ionic bonds – attraction of oppositely charged ions producing electrically neutral compound Covalent bonds – bonds that share electrons Copyright © 2012 Pearson Canada Inc.

The Structure of Minerals Copyright © 2012 Pearson Canada Inc.

The Structure of Minerals A mineral consists of an ordered array of atoms chemically bonded to form a particular crystalline structure Polymorph – some elements can join in more than one geometric arrangement Chemical composition stays the same Physical properties differ Example: diamond and graphite Copyright © 2012 Pearson Canada Inc.

Diamond and graphite are polymorphs of carbon. The Structure of Minerals Diamond and graphite are polymorphs of carbon. Copyright © 2012 Pearson Canada Inc.

Physical Properties of Minerals Crystal habit (shape) External expression of the orderly internal arrangement of atoms Crystal growth is often interrupted because of competition for space and rapid loss of heat Copyright © 2012 Pearson Canada Inc.

Physical Properties of Minerals Lustre Appearance of a mineral in reflected light Two basic categories Metallic Nonmetallic Other terms, such as vitreous, silky, or earthy, are used to further describe nonmetallic lustre Copyright © 2012 Pearson Canada Inc.

Physical Properties of Minerals Colour Often obvious (yellow, pink etc) but not diagnostic if used for ID alone. Slight impurities can produce strong colour variations. Example: Quartz – can be clear, white, rose, smoky, purple etc. Copyright © 2012 Pearson Canada Inc.

Quartz (SiO2) exhibits a variety of colours as in the purple amethyst. Physical Properties of Minerals Quartz (SiO2) exhibits a variety of colours as in the purple amethyst. Copyright © 2012 Pearson Canada Inc.

Physical Properties of Minerals Streak Colour of a mineral in its powdered form when rubbed on an unglazed porcelain tile (streak plate) Hardness Resistance of a mineral to abrasion or scratching All minerals are compared to a standard scale called the Mohs scale of hardness Copyright © 2012 Pearson Canada Inc.

Physical Properties of Minerals Copyright © 2012 Pearson Canada Inc.

Physical Properties of Minerals Cleavage Tendency to break along planes of weak bonding Produces flat, shiny surfaces Described by resulting geometric shapes Number of planes Angles between adjacent planes Copyright © 2012 Pearson Canada Inc.

Physical Properties of Minerals Fracture Absence of cleavage when a mineral is broken Conchoidal fracture – breaks to form smooth curved surfaces like broken glass Copyright © 2012 Pearson Canada Inc.

Physical Properties of Minerals Specific gravity Ratio of the weight of a mineral to the weight of an equal volume of water Average value is approximately between 2.5 and 3 Copyright © 2012 Pearson Canada Inc.

Physical Properties of Minerals Other properties (“special properties”) Magnetism Reaction to hydrochloric acid Malleability Double refraction Taste Smell Elasticity Copyright © 2012 Pearson Canada Inc.

Mineral Classes Nearly 4000 minerals have been identified Rock-forming minerals A few common minerals that make up most of the rocks of Earth’s crust Composed mainly of the 8 elements that make up over 98% of the continental crust Copyright © 2012 Pearson Canada Inc.

Mineral Classes Copyright © 2012 Pearson Canada Inc.

Mineral Classes The Silicates Most common mineral group Basic building block is the silicon-oxygen tetrahedron Four oxygen ions surrounding a much smaller silicon ion to form a more complex ion Copyright © 2012 Pearson Canada Inc.

Mineral Groups More complex Silicate structures Tetrahedra are linked together to form various structures including: Single chains Double chains Sheet structures Copyright © 2012 Pearson Canada Inc.

Common Silicate Minerals Ferromagnesian (dark) silicates Olivine group Pyroxenes – includes augite Amphiboles Biotite Copyright © 2012 Pearson Canada Inc.

Common Silicate Minerals Nonferromagnesian (light) silicates Mica Group Muscovite is the common light coloured mica Feldspar Orthoclase (potassium feldspar) Plagioclase Quartz Clay Copyright © 2012 Pearson Canada Inc.

Mineral Classes Important nonsilicate minerals Several major groups exist including Oxides Hydroxides Sulphides Sulphates Native Elements Halides Carbonates Phosphates Copyright © 2012 Pearson Canada Inc.

Mineral Classes Copyright © 2012 Pearson Canada Inc.

Gemstones Copyright © 2012 Pearson Canada Inc.