Earth Science Notes MINERALS

Objectives I can… Identify and describe the criteria for crystals classification Explain the concept of the Unit Cell and tell why it is necessary in explaining mineral structures Determine the identity of minerals based ont their properties.

Definition of a Mineral A mineral is naturally occurring, inorganic, homogeneous solid with a definite chemical composition Has ordered atomic arrangement.

Five parts to this definition Naturally occurring – not man made, may be found on earth, space, or other planets. Inorganic – minerals are not formed by living things but by earth processes.

Five parts to this definition Homogeneous solid – made up with the same atoms throughout the mineral. The Mineral Halite (Sodium Chloride)

Five parts to this definition Definite chemical composition - atoms must occur in the same ratios. Most minerals are ionic compounds – recall ionic compounds have a definite ratio of atoms  aluminum oxide 2:3 ratio (2 Aluminum atoms to 3 Oxygen atoms)

Five parts to this definition Ordered atomic arrangement – must be crystalline – have repeating units Unit cell – the most basic component of a crystal. Glasses, like obsidian, are not minerals

Orderly Atomic Arrangement Crystals: solids where atoms are arranged in an orderly repeating pattern. Front View of Crystal Lattice Enlarged 3-D view of Unit Cell

Orderly Atomic Arrangement Crystal Lattices – repeated unit cells

Orderly Atomic Arrangement Crystal Systems – made up of crystal lattices Types of crystal systems (also see p 64) Cubic Hexagonal Monoclinic Tetragonal Orthorhombic Triclinic

Orderly Atomic Arrangement Unit Cell  Crystal Lattice  Crystal System

Mineral Formation Minerals form as a result of two processes Magma cooling Minerals formed depend on the elements present and the amount of those elements. The size of the mineral crystal depends on the rate at which the crystal cooled.

Mineral Formation Minerals form as a result of two processes Solutions evaporating Solutions have two parts Solute – substance being dissolved Solvent – substance doing the dissolving With some solutions the solvent (water) can be evaporated and the solute (salt) dissolved reappears in crystal form.

Mineral Formation Solutions evaporating to form minerals: the spotted lake (kliluk), situated in osoyoos, Canada, contains one of the highest concentrations of minerals in the world (mainly epsom salts, calcium and sodium sulphates).

Mineral Classification Most mineral groups are based on the elements that are in the mineral. Silicates – vast majority of the earth’s crust. Ex: Quartz and Feldspar Oxides – minerals that have oxygen in them. Ex: Hematite and Magnetite Sulfides – minerals that have sulfur in them. Ex: Pyrite and galena Halide – … have one of the halogens in them. Ex: halite (NaCl) and Fluorite Pure metal elements: Gold, silver, etc

Mineral Identification Physical Properties of minerals allow for accurate identification Hardness Luster Specific Gravity Streak Cleavage Special Properties

Mineral Identification HARDNESS SCALE INDEX MINERAL COMMON OBJECTS 1 Talc 2 Gypsum Fingernail 3 Calcite 4 Fluorite Copper Penny 5 Apatite 6 Orthoclase 7 Quartz Glass 8 Topaz 9 Corundum 10 Diamond Hardness: determine by Mohs Scale

Mineral Identification Luster: reflecting of light The two main types of luster are metallic and nonmetallic. Metallic luster Nonmetallic Luster

Mineral Identification Specific Gravity: Specific gravity is the "heaviness" of a mineral. It is defined as a number that expresses the ratio between the weight of a mineral and the weight of an equal volume of water. Water has a specific gravity of 1.

Mineral Identification Streak: is the color of the powder left on a streak plate

Mineral Identification Cleavage: is the ability of a mineral to break along preferred planes. Fracture: tendency of a mineral to break along curved surfaces without a definite shape

Mineral Identification Special Properties of minerals Transparency Magnetism Tenacity (how tough a mineral is)

Minerals Summary What makes something a mineral? Five characteristics Arrangement and organization of crystal structures Unit Cell  lattices  Crystal systems Formation of Minerals From lava / Solutions Mineral Identification Based on physical properties

Assessment Can I… Identify and describe the criteria for crystals classification Explain the concept of the Unit Cell and tell why it is necessary in explaining mineral structures Determine the identity of minerals based ont their properties.