1. Stoichiometry
Some minerals contain varying amounts of 2+ elements which substitute for each other
Solid solution – elements substitute in the mineral structure on a sliding scale, defined in terms of the end members – species which contain 100% of one of the elements
Iintroduced binary diagrams before, use a ternary example – feldspar, get figure in here…
Go over several examples in class – make sure students understand this – many mneral subclasses differ only in one or the other elemental substitution – garnet as an example may be good – isostructural, two sets of 3 with a ternary substitution
Work into functional difference of solid solution – differentiate between minerals of solid solution and ones in which substitution is less interchangable – why the difference – is this a chemical or environmental reason?

2. Chemical Formulas
Subscripts represent relative numbers of elements present
(Parentheses) separate complexes or substituted elements
Fe(OH)3 – Fe bonded to 3 separate OH groups
(Mg, Fe)SiO4 – Olivine group – mineral composed of % of Mg, 100-Mg% Fe
Go over this example in detail – maybe get a few others together

3. KMg3(AlSi3O10)(OH)2 - phlogopite
K(Li,Al)2-3(AlSi3O10)(OH)2 – lepidolite
KAl2(AlSi3O10)(OH)2 – muscovite
Amphiboles:
Ca2Mg5Si8O22(OH)2 – tremolite
Ca2(Mg,Fe)5Si8O22(OH)2 –actinolite
(K,Na)0-1(Ca,Na,Fe,Mg)2(Mg,Fe,Al)5(Si,Al)8O22(OH) Hornblende
Actinolite series
minerals

4. Compositional diagrams
Fe3O4
magnetite
FeO
wustite
Fe2O3
hematite A Fe O
A1B2C3
C=50%, B=35%, C=15%
A1B1C1 x
A1B2C3 x B C

5. Fe Mg Si
fayalite
forsterite
enstatite
ferrosilite Fe Mg
forsterite
fayalite
Pyroxene solid solution  MgSiO3 – FeSiO3
Olivine solid solution  Mg2SiO4 – Fe2SiO4

6. Minor, trace elements
Because a lot of different ions get into any mineral’s structure as minor or trace impurities, strictly speaking, a formula could look like:
Ca0.004Mg1.859Fe0.158Mn0.003Al0.006Zn0.002Cu0.001Pb Si0.0985Se0.002O4
One of the ions is a determined integer, the other numbers are all reported relative to that one.

7. Normalization
Analyses of a mineral or rock can be reported in different ways:
Element weight %- Analysis yields x grams element in 100 grams sample
Oxide weight % because most analyses of minerals and rocks do not include oxygen, and because oxygen is usually the dominant anion - assume that charge imbalance from all known cations is balanced by some % of oxygen
Number of atoms – need to establish in order to get to a mineral’s chemical formula
Technique of relating all ions to one (often Oxygen) is called normalization

8. Normalization
Be able to convert between element weight %, oxide weight %, and # of atoms
What do you need to know in order convert these?
Element’s weight  atomic mass (Si=28.09 g/mol; O=15.99 g/mol; SiO2=60.08 g/mol)
Original analysis
Convention for relative oxides (SiO2, Al2O3, Fe2O3 etc)  based on charge neutrality of complex with oxygen (using dominant redox species)

9. Normalization example
Start with data from quantitative analysis: weight percent of oxide in the mineral
Convert this to moles of oxide per 100 g of sample by dividing oxide weight percent by the oxide’s molecular weight
‘Fudge factor’ is process called normalization – where we divide the number of moles of one thing by the total moles  all species/oxides then are presented relative to one another