1. Mineral assembly
Most minerals will deal with ionic bonds between cations and anions (or anionic subunits which are themselves mostly covalent but do not dissociate)
Assembly of minerals can be viewed as the assembly of individual ions/subunits into a repeatable framework
This repeatable framework is a crystal or crystalline material
End of class – want to get them thinking about how things are put together as a lead in to looking at symmetry.

2. Mineral Assembly Isotropic – same properties in every direction
Anisotropic- different properties in different directions  most minerals are this type
Assembly of ions from melts, water, or replacement reactions which form bonds
The matrices the ions are in always contain many different ions – different conditions of formation for the same mineral creates differences…

3. Polymorphs
Two minerals with the same chemical formula but different chemical structures
What can cause these transitions??
sphalerite-wurtzite
pyrite-marcasite
calcite-aragonite
Quartz forms (10)
diamond-graphite
Not only from formation but changes in condition after formation can yield transitions between polymorphs – Carbon and quartz are good examples, discuss

4. Complexes  Minerals
Metals in solution are coordinated with ligands (Such as H2O, Cl-, etc.)
Formation of a sulfide mineral requires direct bonding between metals and sulfide
requires displacement of these ligands and deprotonation of the sulfide
Cluster development is the result of these requirements

8. Mineral growth
Ions come together in a crystal – charge is balanced across the whole
How do we get large crystals??
Different mechanisms for the growth of particular minerals
All a balance of kinetics (how fast) and thermodynamics (most stable)
Discuss growth mechanisms

9. Nucleation
Aggregation of molecules builds larger and larger molecules – becomes a nucleus at some point
Nucleus – size of this is either big enough to continue growth or will re-dissolve (Critical Size)
Overall rate of nucleus formation vs. crystal growth determines crystal size/distribution

10. Crystal Shapes Shape is determined by atomic arrangements
Some directions grow faster than others
Morphology can be distinct for the conditions and speed of mineral nucleation/growth (and growth along specific axes)

11. Ostwald Ripening
Larger crystals are more stable than smaller crystals – the energy of a system will naturally trend towards the formation of larger crystals at the expense of smaller ones
In a sense, the smaller crystals are ‘feeding’ the larger ones through a series of dissolution and precipitation reactions

12. Figure 3-17. “Ostwald ripening” in a monomineralic material
Figure “Ostwald ripening” in a monomineralic material. Grain boundaries with significant negative curvature (concave inward) migrate toward their center of curvature, thus eliminating smaller grains and establishing a uniformly coarse-grained equilibrium texture with 120o grain intersections (polygonal mosaic). © John Winter and Prentice Hall

13. Small crystals…
In the absence of ripening, get a lot of very small crystals forming and no larger crystals.
This results in a more massive arrangement
Microcrystalline examples (Chert)
Massive deposits (common in ore deposits)

14. Igneous Textures
Figure Idealized rates of crystal nucleation and growth as a function of temperature below the melting point. Slow cooling results in only minor undercooling (Ta), so that rapid growth and slow nucleation produce fewer coarse-grained crystals. Rapid cooling permits more undercooling (Tb), so that slower growth and rapid nucleation produce many fine-grained crystals. Very rapid cooling involves little if any nucleation or growth (Tc) producing a glass.

15. Topotactic Alignment
Alignment of smaller grains in space – due to magnetic attraction, alignment due to biological activity (some microbes make a compass with certain minerals), or chemical/ structural alignment – aka oriented attachment
Need pictures – neat discussion of ALH8001 meteorite magnetite grains?