Lecture 2_Dr_Li PDF

Chapter 2: Minerals: The Building Blocks of Rocks 2-1  Minerals: The Building Blocks of Rocks Definition of a mineral: Naturally occurring Inorganic Ice is a mineral? Glass is a minera...

Chapter 2: Minerals: The Building Blocks of Rocks 2-1  Minerals: The Building Blocks of Rocks Definition of a mineral: Naturally occurring Inorganic Ice is a mineral? Glass is a mineral? Solid Ordered internal molecular structure Definite chemical composition Definition of a rock: A solid mass of minerals or mineral like matter that occurs naturally Smart Video: mineral VS rock 2-2 The Composition of Minerals Elements Basic building blocks of minerals 118 are known (90 naturally occurring) Atoms Smallest particles of matter Retains all the characteristics of an element 2-3 The Composition of Minerals Atomic structure Nucleus Central region of atom 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 2-4 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 2-5 The Composition of Minerals Bonding Chemical bonds – Strong attractive force forms compounds Ionic bonds – One atom gives up electron(s), and another receives them. These now oppositely-charged atoms attract each other, bond, and become electrically neutral Covalent bonds – bonds that share electrons 2-6  The Composition of Minerals Ionic bonds Covalent bonds 2-7  The Structure of Minerals Mineral Consists of an ordered array of atoms chemically bonded to form a particular crystalline structure 2-8  The Structure of Minerals Polymorph Some elements can join in more than one geometric arrangement Deeply buried, high pressure Chemical composition stays the same Physical properties differ Example: diamond and graphite Shallowly buried, low pressure 2-9 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 2-10 Physical Properties of Minerals Crystal habit (shape) Smart video: MineralScale 2-11 Physical Properties of Minerals Lustre Appearance of a mineral in reflected light Two basic categories: 1. Metallic 2. Non-metallic Other terms, such as vitreous, silky, or earthy, are used to further describe non- metallic lustre 2-12 Physical Properties of Minerals Colour Colour can be obvious (yellow, pink, etc.); but should not be the only diagnostic tool. Slight impurities can produce strong colour variations. Example: Quartz – can be clear, white, rose, smoky, purple, etc. 2-13 Physical Properties of Minerals Quartz (SiO2) exhibits a variety of colours as in the purple amethyst. Video: MineralColor 2-14 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 2-15 Physical Properties of Minerals Streak Colour of a mineral in its powdered form, when rubbed on an unglazed porcelain tile (streak plate) 2-16 Physical Properties of Minerals Hardness Resistance of a mineral to abrasion or scratching All minerals are compared to a standard scale called the Mohs scale of hardness Video: MohsScale 2-17 Physical Properties of Minerals [kə'rʌndəm] ['topæ z] 2-18 Physical Properties of Minerals Cleavage Tendency to break along planes of weak bonding Produces flat, shiny surfaces Cleavage is described as: Number of planes exhibited Angles between adjacent planes Video: IgneousCleavage 2-19 Physical Properties of Minerals Fracture Absence of cleavage when a mineral is broken Conchoidal fracture - breaks to form smooth curved surfaces like broken glass 2-20 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 2-21 Physical Properties of Minerals Other (“special”) properties Magnetism Reaction to hydrochloric acid Malleability Double refraction Taste Smell Elasticity 2-22  Minerals Classes Approximately 4660 minerals have been identified Rock-forming minerals A handful of 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 In order of abundance: oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. 2-23  Mineral Classes The eight most abundant minerals in Earth’s continental crust 2-24  Mineral Classes The Silicates Most common mineral group Basic building block is the silicon-oxygen tetrahedron (SiO4)4- Four oxygen ions surrounding a much smaller silicon ion to form a more complex ion 2-25  Mineral Groups More complex Silicate structures Tetrahedra are linked together to form various structures including: Single chains Double chains Sheet structures 3D framework 2-26 Mineral Groups Types of silicate structures 2-27 Mineral Groups 2-28  Common Silicate Minerals Ferromagnesian (dark) silicates Minerals containing ions of iron and/or magnesium Most common are: Olivine Pyroxenes (most common is augite) Amphiboles (most common is hornblende) Biotite Garnet 2-29  Common Silicate Minerals Nonferromagnesian (light) silicates Minerals containing various amounts of aluminum, potassium, calcium, and sodium Most common are: Muscovite Feldspar Orthoclase (potassium feldspar) Plagioclase Quartz (silica) Clay (variety of complex minerals that have a sheet structure) (e.g., kaolinite) 2-30 Common Silicate Minerals 2-31  Mineral Classes Important non-silicate minerals Several major groups exist including Oxides Hydroxides Sulphides Sulphates Native Elements Halides Carbonates Phosphates 2-32 Mineral Classes 2-33  Gemstones Gemstones were once erroneously classified by colour. We now classify based on composition. 2-34