Mineralogy Flashcards
What causes Isochromes?
Minerals that are thick or have high birefringence.This is because retardation and interference color depends on Thickneed and birefringence.
What is the retardation of an uniaxial or Biaxial mineral when light follows an optic axis?
Zero retardation
Name 3 common polymorphs of serpentine
Mg3Si2O5(OH)4
- Lizardite
- Antigorite (after Antigorio in Italy
- Chrysolite (from the greek word for golden abd fiber)
Give give 2 examples of Order-Disorder rnxs in Dolomite and Calcite
- Cation disorder in Dolomite
- Anion disorder in Calcite
What importance has the Order-disorder rxn of Calcite and Dolomite?
- Carbonates can carry C into the Earth
- Important in the C-cycle, CCS
What is a Polymorph?
- Same Chemical Composition but different structures (e.g., stishvite (tetragonal), low quartz (trigonal), etc; water, ice, & steam; calcite &aragonite)
What is a Isomorph?
- Same structure but different Chemical Composition (e.g.,CaCO3 Calcite, MgCO3 magnesite, both hexagonal))
Waht is a Solid solution?
Is a homogeneous mineral of variablre composition (ie. a continuous range of chemistries) and communly the same structure (e.g. olivine (forsterite-fayalite), plagioclase (albite-anorthite)
It is possible by isomoerphos substitution of one element in the crystal structure to occur
in terms of symmetry
What is order-disorder?
- Can be considerd as a variety of polymorphism. The two structures are related, but the ordered form (low temp) has a lower symmetry than the disorder form (high temp).
what are two types of phase transitions?
- Displacive = change in symmetry, no breaking of bonds, rapid transitions (dashed lines)
- Reconstructive = breaking & reforming of chemical bonds new structural arrangement, sluggish (solid lines)
What mineral has the highest refractive index and density in SiO2?
- Stishovite
It is formed under great pressure so has a more dense crystal structure. Good property.
what are the 2 most abundant minerals in the Earth’s crust?
Next to Feldspar, Quartz is the most abundant mineral in the Earth’s crust
ne… and Si-
With what minerals Quartz incompatible with?
Incompatible with nepheline and other Si-poor minerals (e.g. sodalite, cancrinite) are therefore absent from undersaturated igneous rock)
What Silicate minerals are very rare in nature and associated with meteor impact craters?
coesite and stishovite
Can also be brought up by Kimbelites to the surfice.
What minerals can occur in association extrusive or volcanic equivalents of granites and related rocks? ?
tridymite and cristobalite
Rapid cooling preserves these polymorphs
Give 6 distinguishing features of Quartz
- Lack of color, cleavage, visible twinning
- Low relief, weak birefringence
- Uniaxial interference figure
- Positive Optic sign
- Lack of alteration
- Undulatory extinction in strained rocks
What is the relation between Temperature and Pressure with density in polymorphs?
- High-temperature polymorphs have low densities
- High-pressure polymorphs have higher densities
why micas have cleavages?
The basal cleavage in Micas occur because there is only weak K bonding between the structural sheets of the mica structure. Movement , or cleavage can occur easily along those planes of weak bonds.
Give at least 3 distinguish features of Micas
- Platy morphology
- Perfecrt basal cleavage (gama aprox. perp. to their perfect 001 cleavage)
- Flexible sheets
- Negative Biaxial
- Coloured Micas are strongly Pleochroic (biotite)
- Muscuvite & phlogopite: absence of defects and inclusions
- Biotite: colored, inclusions and pleochroic halos, Higer refractive index than other micas.
Which mica has the highest 2V?
Biotite (highest), than muscavite and Phlogopite (lowest) last
