Lecture three part 1 Flashcards
What are nesosilicates
Minerals with isolated SIO4 tetrahedra in the Structure
What compounds are absent in nesosilicates
Compounds with alkali elements such as sodium and potassium
What are some Physical properties of nesosilicates And why do they exist
Nesosilicates have poorly developed cleavage they are relatively hard and they have higher density than other silicate structure types because their atomic packing is notably dense
What are the two main groups of nesosilicates
The olivine group the Garnet group
What type of Silicates are olivines
Nesosilicates
What type of silicates are garnets
Nesosilicates
What are the four main types of olivine
Forsterite, fayalite, tephroite, and Monticellite.
What is peridot
Semi-precious gem quality forsterite
What is the chemical composition of forsterite (Fo)
Mg2SiO4
What is the chemical composition of Fayalite (Fa)
Fe2SiO4
What is the chemical composition of tephroite (te)
Mn2SiO4
What is the chemical composition of Monticellite (Mo)
CaMgSiO4
What is a solid solution
The Ability of one solid end member To dissolve into another with complete miscibility
Between which two end members does Fayalite exist in complete solid solution with
Forsterite and tephroite
Can a solid solution exist between forsterite and tephroite
No
Can a solid solution exist between monticellite and forsterite
No
With what symmetry do the end members of Olivine crystallize
Orthorhombic symmetry
What effect does temperature have on interstitial sites
It increases them
What effect does temperature have on interstitial sites
It decreases them
At what temperature does Forsterite melt
1890 degrees
At what temperature does Fayalite melt
1200
What is a phase diagram
A diagram which displays the changes of phase of a material under related conditions such as temperature vs pressure or temperature vs composition
What is the liquidus line in a phase diagram
The line across which a material transitions from a complete liquid to a partial solid /partial liquid
What is the solidus line in phase diagrams
The line across which a material transitions from partial liquid/partial solid to completely solid
What are the residual liquids during the crystallization process called
Restites
Under what conditions does olivine undergo serpentinization
Hydrothermal events and low temperature
What is hydrothermal activity
Any process associated with igneous activity involving heated or superheated water
What is serpentinization
The process whereby weathered olivine alters into serpentine
What are the three polymorphs or serpentine
Lizardite, crysolite, and antigorite
Does serpentine occupy a greater or smaller volume than Olivine
A greater volume, it causes olivine to fracture
What is the oxidized form of olivine called
Iddingsite, though it is now known to consist of haematite and periclase (MgO)
What is the mantle transition zone
The portion of the mantle between 500 and 670 km which separates the upper from the lower mantle
What does Olivine change into in the Transition Zone
The more dense Wadsleyite and then to a spinel structure called ringwoodite
What is a spinel structure
A cubic mg-fe aluminum oxide pseudomorphed with other high density minerals
What are the hand specimen properties of Olivine
Short prismatic crystals with a hardness of 6-7 and a green colour. It has no streak and a transparent vitreous lustre. It does not usually display cleavage, and it fractures in a conchoidal manner
What pleochoism does olivine display.
Usually colourless. Darker colours represent higher iron content
What is the habit of Olivine
Usually anhedral grains in intrusive and metamorphic rocks. Equant or elongated euhedral grains in extrusive volcanic rocks.
What is the relief of Olivine
High
Does Olivine have cleavage
Not observed
What is the birefringence of olivine
0.03 - 0.05 up to third order
What is the interference figure of Olivine.
Biaxial, positive or negative, 2v = 46 -98
What is the extinction of olivine
Parallel to crystal outlines
Does olivine have twinning
Not usually
What is the general formula of a garnet
X3Y3(SiO4)3
What are the 6 common types of garnet
Pyrope, Almandine, Spessartine, Grossular, Andradite, Uvarovite
What is the most common kind of Garnet
Almandine
What is the chemical composition of Pyrope (Py)
Mg3Al2(SiO4)3
What is the chemical composition of Almandine (Al)
Fe3Al2(SiO4)3
What is the chemical composition of Spessartine (sp)
Mn3Al2(SiO4)3
What is the chemical composition of Grossular (gr)
Ca3Al2(SiO4)3
What is the chemical composition of Andradite (An)
Ca3Fe2(SiO4)3
What is the chemical composition of Uvarovite (Uv)
Ca3Cr2(SiO4)3
What are pyrope, almandine, and spessartine sometimes referred to as?
Pyralspites
What are Uvarovite, grossular and andradite sometimes referred to as?
Ugrandites
What symmetry do garnets crystallize with
Cubic symmetry
Between what two end members does almandine exist in complete solid solution with
Pyrope and Spessartine
Is there a complete solid solution between pyrope and spessartine?
No only a limited solid solution
Do pyralspites and ugrandites exist in solid solution
No there is no continuous solid solution between these two groups of Garnet
Is there solid solution between the end members of ugrandites
Yes extensive solid solution exists between grossular, andradite, and Uvarovite
