Earth Materials - Mineral Genesis (Exam 2)

What are the 4 main ways minerals can form?

solid-solid reactions, crystallization from a liquid, deposition from a vapor (no intermediate liquid), precipitation from a fluid such as H2O or CO2

what does polymorph mean

minerals in different forms with the same composition but different structures

what is polymorphic transformation/solid-solid reaction

when one polymorph transforms into another

what controls the conditions which a particular polymorph is stable?

temperature and pressure

name 3 polymorphs of SiO2

quartz (trigonal), tridymite (triclinic), cristobalite (tetragonal)

name 3 polymorphs of Al2SiO3

kyanite, sillimanite, andalusite

draw the Al2SiO3 phase diagram

what are the 3 energy states

unstable, stable, and metastable

what is Gibbs Free Energy

measure of chemical energy, all chemical systems tend naturally toward states of minimum free energy

At higher temperature, the phase with larger entropy (S) will have (higher/lower) G

lower

at higher pressure, the phase with the lower volume will have the (higher/lower) G

lower

smallest volume means (highest/lowest) pressure

highest

largest volume means (highest/lowest) pressure

lowest

largest entropy means (highest/lowest) temperature

highest

smallest entropy means (highest/lowest) temperature

lowest

which mineral has the smallest volume?

stishovite

which mineral has the largest volume?

tridymite

which mineral has the smallest entropy?

alpha quartz

which mineral has the largest entropy?

liquid

what are the 2 polymorphs of CaCO3

aragonite and calcite

what are the 3 types of polymorphic transformations?

reconstructive transformation, displasive transformation, order-disorder

give the mineral names of an example of solid-solid reaction involving more than one phase

albite, jadeite + quartz

which indicates higher pressure?

jadeite + quartz

which has a smaller volume?

jadeite + quartz b/c the pressure is higher

what is nucelation

formation of new minerals

why do displasive and order-disorder transformation NOT require nucleation?

bonds stretch or shrink but do not break in displasive transformation (beta-quartz to alpha-quartz)

atosm order on different crystallographic sites in order-disorder (sanidine to orthoclase to microcline)