Dynamic Interior L3 Flashcards
What is a mafic mineral?
Dark coloured minerals rich in magnesium and iron.
What is a felsic mineral?
Light coloured minerals rich in silicon and aluminium.
How thick do thin sections have to be so that the minerals will transmit light?
30 micrometres
What does plane-polarised light (ppl) do and what is the name of the colours produced?
- Polarised light travels through a crystal and interacts with the atoms
- It is slowed down and parts of the colour spectrum may be absorbed and so PPL images may either be coloured or colourless
- Absorption colours
What does cross-polarised light (xpl) do and what is the name of the colours produced?
- Light travels through the crystal and passes through a polariser
- The light paths are recombined through a lens
- The recombined light paths interact and produce interference colours
How do silicate tetrahedra carry out polymerisation and what can be formed?
The sharing of one or more of their apical oxygen atoms to form chains, rings and sheets
What is homovalent substitution?
The substitution of an ion for another ion of the same charge
What is coupled substitution?
The substitution of a pair of ions for another pair of ions with equal charge.
Give an example of coupled substitution?
Mg2+ + Ca2+ = Na+ + Al3+
What is an isomorph?
Minerals with similar structures but a different chemical composition
What is the olivine group’s chemical composition?
(Mg,Fe)2SiO4
What mineral group has the chemical composition (Mg,Fe)2SiO4?
Olivine group
Give an example of an olivine end member with its chemical composition.
Forsterite, Mg2SiO4
What crystal system is olivine?
Orthorhombic
What are common characteristics of olivine in thin section?
Common irregular fractures
High relief
Colourless to pale yellow/yellow orange in PPL
