Download Minerals Outline •Definition •Structure •Physical Properties

Minerals Outline
•Definition
•Structure
•Physical Properties
•Classification
•Resources
Minerals: Building blocks of rocks
•Definition of a mineral:
•Naturally occurring
•Inorganic crystalline solid (for most part)
•Ordered internal molecular structure
•Definite chemical composition
•Definition of a rock:
•A solid aggregate or mass of minerals
Physical Property of Minerals
•Crystal Form
–External expression of orderly internal arrangement (structure) of atoms,
chemical bonds
–Ionic compounds, internal arrangement determined by size of ions
–Crystal growth can be interrupted by:
•Lack of space
•Lack of material
•Rapid loss of heat
Physical properties of minerals
•Crystal Form
•External expression of the orderly internal arrangement (structure) of atoms
•Crystal growth is often interrupted because of competition for space and rapid
loss of heat
Structure of minerals
•Polymorphs
•Two or more minerals with same chemical composition but different crystalline
structures (shapes)
–The transformation of one polymorph to another = phase change
Diamond and graphite –
polymorphs of carbon
Physical properties of minerals
•Luster
–Quality of reflected light (shine)
–Two very general categories
–Metallic
–Nonmetallic
–Other terms are used : vitreous (glassy), silky, resinous, pearly, or earthy
Pyrite (fool’s gold) displays metallic luster
Physical properties of minerals
•Color
•Generally unreliable
•Can be highly variable due to slight changes in chemistry
•Exotic colorations of some minerals are gemstones
•Streak
•Color of mineral in powdered form
•Helpful in distinguishing different forms of the same mineral
•Can be highly useful w/metallic luster minerals
•To obtain streak, scratch on ceramic plate
•Hardness
•Resistance of a mineral to abrasion (scratching), relative hardness
•All minerals compared to a standard scale called Mohs Scale of Hardness
–Scale=exponential in character
»i.e. diamond is not 2x as hard as apatite, but is more like 16-17xs
•Cleavage
•Tendency to break along planes of weakness
•Produces flat, shiny surfaces
–Easy to confuse with crystal growth structures!
•Described by resulting geometric shapes
–Number of planes
–Angles between adjacent planes
•Fracture
•Absence of cleavage in broken mineral
Conchoidal fracture
Other properties
•Magnetism
•Specific Gravity
•Reaction to hydrochloric acid
•Malleability
•Double refraction
•Taste
•Smell
•Elasticity
Classification of Minerals
•Nearly 4000 minerals have been identi-fied on Earth!!!
•Few are important
•Rock-forming minerals
•In crust, minerals combine to form rocks
–Only a few dozen
•Silicates
•Most important mineral group
–Comprise most rock-forming minerals
–Very abundant due to large amounts of silicon and oxygen in Earth’s crust
•Basic building block = silicon-oxygen tetrahedron molecule
–Four oxygen ions surrounding a much smaller silicon ion
•Silicate structures
•Single tetrahedra = linked together to form various structures including
–Isolated tetrahedra
–Ring structures
–Single and double chain structures
–Sheet or layered structures
–Complex 3-dimensional structures
Common Silicate Minerals
•Olivine
–High temperature Fe-Mg silicate
–Individual tetrahedra linked together by iron and magnesium ions
–Forms small, rounded crystals with no cleavage
•Pyroxene Group
–Single chain structures involving iron and magnesium
–Two distinctive cleavages at nearly 90 degrees to each other
–Augite = most common mineral in pyroxene group
•Amphibole Group
–Double chain structures involving a variety of ions
–Two perfect cleavages exhibiting angles of 124 and 56 degrees
–Hornblende = most common mineral in amphibole group
•Mica Group
–Sheet structures that result in one direction of perfect cleavage
–Biotite = common dark colored mica mineral
–Muscovite = common light colored mica mineral
Feldspar Group
–Most common mineral group
–3-dimensional framework of tetrahedra exhibit two directions of perfect
cleavage at 90 degrees
–Orthoclase (potassium feldspar) and Plagioclase (sodium and calcium feldspar)
= two most common members
•Clay minerals
–Clay = general term describing a variety of complex minerals
–Clay minerals = sheet or layered structure
–Most originate as products of chemical weathering
»Resulting in fine powdery grains
•Quartz
–Very common mineral group
–3-dimensional framework of tetrahedra with no discernable cleavage
Several Non-silicate Minerals Include:
Carbonates
–Consists of Carbon and Oxygen
–Primary constituents in limestone and dolostone
–Calcite (calcium carbonate), Aragonite (calcium carbonate), and Dolomite
(calcium-magnesium carbonate) are the two most important carbonate minerals
–Calcite=one of the most common minerals on earth
Several Non-silicate Minerals Include:
Oxides
–Consists of Oxygen and 1 or 2 metals
–Mined and refined for pure minerals for commercial use
–Can form from oxygen found in atmosphere or elsewhere
Native Minerals
–Only made of one, single element
–Over 100 known
–Usually concentrated in vein deposits and by hydrothermal fluids
Sulfides
–Consists of metals bonded with Sulfur
–No oxygen
–Many are mined and refined for commercial use
–Tend to be formed in hydrothermal fluids
Sulfates
–Consists of metals bonded with Sulfur and 4 Oxygens
–Used for drilling and building
–Tend to be formed in surface environments
Halides
–Compounds with Halogens (e.g. chlorine)
–Examples include fluorite and Halite
The periodic table
•Many nonsilicate minerals have economic value
•Examples
–Hematite (oxide mined for iron ore)
–Halite (halide mined for salt)
–Sphalerite (sulfide mined for zinc ore)
Mineral resources
Reserves are already identified deposits
•Known deposits that are not yet economically or technologically recoverable
Mineral resources
•Ore
–Useful metallic mineral that can be mined at profit (key)
–Must be concentrated above its average crustal abundance
–Profitability may change because of economy
Mining Can Hurt the Environment
•Acid Mine run-off
–Mining spoils and tailings
•Spoils=noneconomic
•Tailings=left over from processing ore, fine-grained
•Often contain pyrite, toxic substances
•Pollution
•Large Scale destruction of land
•Dangerous to people and animals
•Expensive
•Reclamation