Ch 4a: Minerals Flashcards
Minerals
naturally occurring, inorganic, fixed composition or range of composition, solid, repeating atomic structure (crystalline)
Atoms and Elements
Theres about 90 naturally occurring elements in the periodic table.
Top 8 elements in the Earth
Iron (most in the core), Oxygen, Silicon, Magnesium, Nickel (most in the core), Sulphur, Calcium, Aluminum
Top 8 elements in the Crust (oceanic order)
Oxygen, Silicon, Aluminum, Iron, Magnesium, Calcium, Potassium, Sodium
Top 8 elements in the Crust (surface order)
Oxygen, Silicon, Aluminum, Iron, Calcium, Magnesium, Potassium, Sodium
_____ are responsible for chemical properties
Electrons. Unfilled outer shells are unstable created by losing, gaining or sharing electrons.
Ions
atoms that have gained or lost electrons. Cations (+), Anions (-)
Three main types of bonding:
ionic, covalent, van der Waals
Ionic:
Attraction between ions of opposite charge. Transfer of electrons. Most minerals (90%)
Covalent:
Very strong attraction between two or more atoms, share electrons.
Covalent - Metallic:
Hybrid bonding, electrons are free to move among the ions; electrical glue. Great conductors, really ductile, flexible bonds
Van der Waals
force of attraction between temporary dipole molecules
Bonding in Crystals:
produces a crystal lattice: regular arrangement, controls many mineral properties
Mineral Properties:
crystal habit, hardness, cleavage, fracture, color, streak, lustre, others
Crystal Habit
Shape, reflects internal crystal structure (constant inter-facial angles). Given time and space can grow very large, limited space = minerals will interlock.
eg. Quartz = hexagonal or euhedral
Hardness
Measure of the ease with which the surface can be scratched. Mohs Hardness scale.
Mohs Hardness Scale:
devised by Austrian Friedrich Mohs , not a linear scale
Cleavage
Tendency of the mineral to break along planar surfaces.
Cleavage face (plane):
Weak bond between atoms or molecules, number of planes and geometric pattern of the cleavage is diagnostic
Cleavage and Bonding
ability to cleave varies inversely with bond strength.
Polymorphism
Ability of a solid material to exist in more than one form or crystal structure. Common in metamorphic rocks.
eg. Diamonds and Graphite.
Fracture
Tendency of the mineral to break along irregular surfaces of weakness. Fractures from impurities
Color
Interaction of light within the mineral, controlled by composition. NOT A DIAGNOSTIC TRAIT.
Streak
Color of the mineral when powdered. The impurities vanish. More diagnostic than color.
Lustre
Sheen or reflectivity, quality of reflected light from a mineral surface.
Metal’s Lustre
metallic
Non-metals lustre
Earthy, glassy, resinous, pearly
Other properties
Magnetism, effervesce in HCl acid, iridescence (play of colors due to internal reflections), fluorescence (glow under UV)
Elements in the Crust
rock-forming minerals: most are combinations of Si and O with the six metals. SILICATE MINERALS
Magnetism
Means theres a type of iron
Iridescence
Opal Labradorite
Silicates (SiO4)^-4
most abundant minerals in the Crust. Divided based on crystal structure
Silicates
nesosilicates, cyclosilicates, inosilicates, phyllosilicates, tectosilicates
Nesosilicates:
isolated tetrahedra
eg. Olivine
Cyclosilicates
Rings
eg. Emerald
Inosilicates
single or double chains
eg. Pyroxene groups/Amphibole group
Phyllosilicates
Sheets
eg. Mica
Tectosilicates
Framework
Quartz
SiO2, most common single mineral. Low temperature mineral, resistant to weathering and erosion doesn’t break down easily.
Feldspar Grup
Most abundant mineral group in crust. Contain Al,O,Si,Na,K,Ca. 3D frameworks
Ferro-magnesium silicates
Main constituent of the mantle, contain iron and magnesium. Chain, ring, and sheet silicates. Dark specs in the rock, tend to form at higher temperatures, less stable at Earth’s surface. Breaks down and turns into clay.
Micas
Sheet silicates, splits easily, varies from white (Al-rich) to black (Fe-rich)
Clays
Form sheets that can absorb or lose water, by-product of weathering of other minerals.
Non-silicates
Do not contain Si, may form compounds or single elements.
Carbonates, Sulphates, Sulphides
Carbonates (CO3)^-2
chemically precipitated out of seawater by organisms (Limestones).
eg. Calcite, Dolomite
Sulphates (SO4)^-2
Forms from a tetrahedron. Indicates a water environment
eg. Gypsum, Anhydrite
Sulphides (S^-2)
No oxygen, important ore minerals (copper, zinc, lead and nickel). Streak works well.
eg. Pyrite, sphalerite, galena
Oxides
oxygen is ionically bonded to metallic cations, oxides contain oxygen
Hydroxides
contain hydroxyl
Oxides and hydroxides examples:
eg. Hematite, Magnetit, Brucite
Halides:
contain halogens, chemically precipitated.
eg. Evaporites:
Halite (rock salt), Sylvite (potash)
Native Elements
No processing involved. Neutral atoms, no ions. Metallic, covalent.
Native Elements - Metallic
Metallic elements held together by metallic bonding.
Precious (gold, silver), base (copper, lead, zinc)
Native Elements - Covalent
Semi-metallic (Bismuth), Non-metallic (diamond)
