Crystal Growth Flashcards
Nucleation
First stage of growth, can only commence after a nucleus/seed has formed.
Supersaturation
Usually required in solution for nucleation. Achieve by changing a mechanism (concentration, T and/or P).
Competing Tendencies for Nucleation and Growth in Cooling Magma
Thermal vibrations and attractive forces.
Crystal Habit
External appearance of crystal and it’s combination of crystal forms. example: equant, fibrous, scaly, tabular.
1) Euhedral
2) Anhedral
3) Subhedral
1) crystals display perfect polyhedral surfaces with regular interfacial angles.
2) Crystals with irregular surfaces.
3) Mixture of above two.
Twinning
Symmetrical intergrowth of two or more crystals of the same substance. Considered a type of planar defect.
Composition Surface
Surface that twinning are united.
Twin Plane
Reflection by a mirror plane
Twin Axis
Angular 180 degree rotation axis common to twinning crystals.
Twin Center
Inversion about a point
Contact Twin
Have regular composition separating two individuals. Twins produced by either reflection or rotation.
Penetration Twin
Made up of interpenetrating individuals having an irregular composition surface. Usually defined by a twin axis direction.
Polysynthetic Twin
Multiple twins that have three or more crystals twinned AND all composition surfaces are parallel.
Cause of Twinning -Growth Twins
Error in stacking of unit cells when crystal first starts to grow leads to twinning.
Causes of Twinning -Transformation Twin
Variations in T and P stresses lattice, warping to relieve stress leads to twinning.