L3 introduction to minerals Flashcards
What is a mineral?
A naturally occurring inorganic solid;
with an ordered internal structure;
made up of a regular and repeating arrangement of atoms;
and a definite (but not fixed) chemical composition
Can gemstones be produced by industrial processes?
yes as there are synthetic gemstones
What synthetic gemstones be used for?
Jewellery
Communications
Laser tech
Micro-electronics
Abrasives
How do industrial processes mimic natural processes to produce gemstones artificially?
crystal growth under high temp
(high pressure- synthetic diamonds)
What states are almost all minerals in?
solid (rare exception liquid mercury)
What will the solid structure of minerals look like generally?
regular repeating three-dimensional patterns of atoms, ions or ionic groups
What is the chemical compositions of minerals like?
definite but not fixed
Is the ratio of cations (+) to anions (-) fixed or variable?
fixed
What can make the ratio of cations to anions in minerals more complex?
where different metal cations can substitute into the same structure
Where does crystallisation of minerals occur from?
Magma
What is magma? (not definition but what actually is it as a liquid)
high temperature liquid (high kinetic energy no solid stable)
What happens when magma cools and kinetic energy decreases? (crystallisation from magma)
atoms slow down enough for bonds to persist
Allows nucleation of crystals from melt
What can lead to larger more well formed crystals from magma?
if high temperatures remain, magma
partially molten, atoms still quite
mobile and move toward the surfaces of growing crystals
What happens if there is rapid cooling of magma? (crystal formation)
smaller less well formed crystals
What are pegmatite veins?
found around granites with exotic
minerals hosting rarer elements that don’t fit in “normal” silicate minerals
What are pegmatite veins often targeted for?
mineral exploitation
How can very water rich melts and magma bodies at late stage cooling create large crystals?
low viscosity
leading to very rapid crystal growth rate
What processes are the cause of crystal formation in solid state?
metamorphic
How can minerals form from metamorphic processes?
chemical reactions replacement of of current minerals with new ones
How are atoms transported to sites of new mineral creation? (metamorphic crystal formation)
bonds broken and atoms migrate by solid state diffusion or transported short distances by intergranular fluids
How is the mineralogy of metamorphic rocks more diverse?
includes minerals found in both other rock types plus high pressure / high temperature equivalents
How can minerals form from precipitate?
Precipitation from aqueous solutions containing ions of different sorts
What is solubility?
how much solid material dissolves per unit of solute
What physical conditions can change solubility?
most substances are more soluble in water at higher temperatures and higher pressures
What might a decrease in temp do to solubility?
decrease in temperature (or pressure) may lead to over saturation, nucleation, and
precipitation of solid (mineral) phase
What might loss of solute do to solubility?
may increase concentration of ions until nucleation and precipitation starts (evaporite minerals)
How are minerals grouped?
basis of chemical composition based on the dominant anion or anion complex
How many recognised minerals are there?
4150
how many common rock forming minerals are there?
90
What are native elements?
composed of a single element
What does it mean to metals weather?
react with oxygen and form their oxide
What metals are usually found in native form?
Generally only less reactive metals, such as gold, silver, copper, platinum
What does polymorphism mean?
same chemistry but different structure
What is the structure of graphite like?
carbon atoms in sheets; weak bonding -> soft
How is diamond formed?
formed at very high pressures
What is the structure of diamonds like?
carbon atoms densely packed into tetrahedral framework -> hard and strong
What are oxides?
Metal cations ionically bonded to oxide anions
What are the oxide groups?
Simple oxides
Hematite group
Rutile group
Spinel group
What will simple oxides formulae look like? (X= cation)
X2O
XO
What do hematite group oxides formulae look like?
X2O3
What do Rutile group oxides formulae look like?
XO2
What do spinel group oxides formulae look like?
XY2O4
What is the composition of hydroxides?
Metal cations combined with hydroxide (OH-) anions
How do hydroxides usually form?
at lower temperatures & are softer than oxides
What are hydroxides usually the product of?
Weathering or degradation
Where does limonite form?
fresh waters
bogs
What is gibbsite an important component of?
aluminium bauxite ore
What are sulphides?
metal cations ionically bonded to sulfur anions
What type of condition’s are sulphides indicative of?
reducing
What is pyrite?
fools gold
What conditions does pyrite form in?
sedimentary conditions under reducing / low oxygen environment
What is the composition of sulphates?
Metal cations ionically bonded to sulphate anions
What is the most important and common sulphate?
gypsum
What is gypsum economically important for?
component of plaster
Where does gypsum form?
primary evaporite minerals, formed in tropical restricted marine environments
What are the 3 forms of gypsum?
satin spar (fibrous),
selenite (transparent),
alabaster (fine-grained, massive form)
What is the composition of halides?
Metal cations and halogen anions
What 2 types of halides are common in sedimentary rock?
halite
sylvite
How is halite typically found?
rock salt (evaporite from salt lake)
What is fluorite?
A halide associated with metal ores (zinc)
What is the composition of carbonates ?
Metal cations ionically bonded to carbonate anions
What is the formula for oxide anions?
O2-
How does alteration of minerals occur?
through oxidation and reaction with hydrous fluids
or
Hydrothermal fluids
What is formed through mineral alteration?
forms secondary minerals that reflect original mineral and alteration process
What is the formula for hydroxides anions?
OH-
What is the formula for sulphide anions?
S2-
What is the formula for sulphate anions?
SO42-
What are some examples of halogen anions?
Cl-
F-
Br-
I-
What are the 3 most important and common forms of carbonates?
Calcite
Aragonite
Dolomite
What is the formula for for carbonate anions?
CO32-
What is the formula for metal cations involved in carbonate formation?
Ca2+
What is calcite?
CaCO3
dominant form of calcium carbonate
What is aragonite?
CaCO3
polymorph of calcite
What is aragonite like compared to calcite?
low temperature and metastable
Often biogenic
What is dolomite?
(CaMg(CO3)2)
associated with digenesis in reducing conditions
What determines the minerals that make up the rocks in the mantle and crust?
the elements that dominate the mantle and crust
What are silicates composed of?
Si
O
What are some examples of silicates?
Feldspar
Mica
Olivine
Quartz
Pyroxene
Which mineral group is the most abundant in earths surface?
Silicates
What will happen if the abundance of minerals isnt enough to form a specific rock/crystal?
another will be formed which matches the conditions and abundance
What are igneous rocks made up of?
an assemblage of minerals that reflect the chemistry of the magma(s) that formed them, and with crystal sizes that reflect their cooling history
How are metamorphic rocks formed?
through mineral growth via atomic reorganisation in the solid state
How are sedimentary rocks formed?
from individual mineral grains, produced by weathering and erosion of other rocks, or from biomineralized materials; and/or from direct mineral precipitation
What is an example of the fixed cation to anion ratio?
NaCl 1:1
What is an example of a more complex ratio of cation to anion?
Olivine- as different metallic cations can fit into structure (Mg, Fe) can be either Fe or Mg rich
What will tend to alter the texture of metamorphic rocks?
stress field
local conditions
What are some examples of liquids reaching the solubility limit?
hydrothermal settling
evaporite salt
stalactites and stalagmites
fluorite
What minerals dominate earths crust?
Silicon (27%)
Oxygen (47%)
What is the problem with having a limited number of minerals available?
it limits the ability to produce vast amounts of different rocks
How can gold be found in its native form?
nuggets
veins
How can silver and copper be found in their native form?
dendritic coatings
Why cant all cations fit into the gaps in minerals like olivine?
They might be too big or not have the correct charge to create a stable energy balance
What are the silicate group of minerals built around?
silicate tetrahedral (1 silicon 4 oxygen ionically bonded)
What do silicate tetrahedra combine to create?
a silicate framework (different combinations create different structures)
What is the tetrahedra combination of olivine like?
isolated silicate tetrahedra
What needs to be the case for silicate tetrahedra to be electrostatically neutral?
4- charge must be balanced by positive cations between tetrahedra
What can the cation anion structure of olivine be like?
fixed ratio but there can be 2 cations to one anion (Mg or Fe)
What is the simplest form of a solid solution?
when atoms of 2 different elements can substitute for each other within a mineral structure
What must the atoms for a solid solution be like comparatively?
similar ionic radii
same electrostatic charge
What does having solid solution give olivine?
variable composition restricted and defined by the nature of the holes in the structure
What can happen when oxygens from different tetrahedra bond? (silicate tetrahedra)
they can form chains
What is an example of a single chain silicate tetrahedra?
pyroxene
What is an example of a double chain silicate tetrahedra?
amphibole
What is an example of a sheet formation of silicate tetrahedra?
Mica (
