the rock forming silicate minerals basic principles l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
The Rock Forming Silicate Minerals: Basic Principles PowerPoint Presentation
Download Presentation
The Rock Forming Silicate Minerals: Basic Principles

Loading in 2 Seconds...

play fullscreen
1 / 17

The Rock Forming Silicate Minerals: Basic Principles - PowerPoint PPT Presentation


  • 372 Views
  • Uploaded on

The Rock Forming Silicate Minerals: Basic Principles. Importance of the Silicates. Abundance ~25% of all known minerals Make up ~90% of earth’s crust Composed of dominant elements in earth’s crust (O, Si, Al, Fe, Mg, Ca, Na, K) Rock-forming minerals Economic uses

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'The Rock Forming Silicate Minerals: Basic Principles' - fritzi


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
importance of the silicates
Importance of the Silicates
  • Abundance
    • ~25% of all known minerals
    • Make up ~90% of earth’s crust
    • Composed of dominant elements in earth’s crust (O, Si, Al, Fe, Mg, Ca, Na, K)
    • Rock-forming minerals
  • Economic uses
    • Building construction (brick, stone, morter, glass)
    • Technology (silicon chips)
what are silicates

SiO4

Si2O7

SiO3

Si4O11

Si2O6

Si2O5

SiO2

What Are Silicates?
  • Frameworks based on the linkage of cation centered coordination polyhedron
    • The silica tetrahedra: the building block of the silicate minerals
    • SiO4-4 is the basic unit
the silicates
Frameworks based on the linkage of SiO4-4 tetrahedra

Results in a structurally stable, anion complex

Suitable for the formation of polymers (two or more shared complex ions of the same type)

Charge reaching the cation is exactly 1/2 the charge on the anion

Limited ways in which polymers can form (Pauling’s Rules)

Charge balance in minerals attained by:

Sharing oxygen between adjoining tetrahedra

Linking tetrahedra with other cations

SiO4

Si2O7

SiO3

Si4O11

Si2O5

SiO2

The Silicates
silicates structure
Ratio of Si to O determines structural configuration and is the criteria for silicate classification (subclasses)

Neso: SiO4-4, separate tetrahedra (1:4; Si:0)

Soro: Si2O7-6, double tetrahedra (1:3.5; Si:0)

Cyclo: Si3O9-6 (3 tetrahedra ring), Si4O12--8 (4 tetrahedra ring), Si6O18- 12 (6 tetrahedra ring) (1:3; Si:0)

Si2O6

Si4O11

Si2O5

Si2O7

SiO2

SiO3

SiO4

Silicates Structure
more silicates structure
Ratio of Si to O determines structural configuration and is the criteria for silicate classification (subclasses)

Ino: SiO3-2 (single chain of tetrahedra) (1:3; Si:0), Si4O11-6 (double chain of tetrahedra) (1:2.75; Si:0)

Phyllo: Si4O10-4 (OH)2, sheets of tetrahedra (1:2.5; Si:0)

Tecto: SiO2, three dimensional frameworks (1:2; Si:0)

Si2O6

Si4O11

Si2O5

Si2O7

SiO2

SiO3

SiO4

More Silicates Structure
silicate subclasses
Silicate Subclasses
  • Neso (a)
  • Soro (b)
  • Cyclo (c, d, e)
structural formulas and silicate group minerals
Structural Formulas and Silicate Group Minerals
  • Where do the other cations fit?
  • Coordination polyhedron with oxygen depends on ionic radius
structural formulas and silicates
Structural Formulas and Silicates
  • Describes the structural and chemical relationship between related minerals (mineral groups) through a generalized description of the chemical formula
  • Symbology
    • X = large, weakly charged cations, C.N. >6 (with oxygen)
      • Na, K, & Ca (sort of)
    • Y = medium-sized, 2+ to 4+ cations, C.N. = 6
      • Mg, Fe+2 , Fe+3, Al, Ti, & Ca (sort of)
    • Z = small cations, C.N. = 4
      • Mainly Si+4, but also Al+3
    • W = additional anionic groups
      • OH-, Cl-, F-
  • Results in generic formula for all silicates: XmYn(ZpOq)Wr
t x phase diagrams
T-X Phase Diagrams
  • Diagrams showing the relationship between temperature, composition, and proportion of crystals and liquid in a melt
    • Liquidus: t-x at which first crystals form from a melt
    • Solidus: t-x at which the last melt crystallizes
the solvus and miscibility gaps
Miscibility gap (opposite of solid solution)

Defined by the solvus

Outline of the miscibility gap

Represents the area of a phase diagram where naturally occurring minerals do not occur

The Solvus and Miscibility Gaps
temperature and miscibility gaps
Temperature and Miscibility Gaps
  • Temperature dependant solid solution/ion substitution
    • The extent of ion substitution is dependant on
      • Ionic radius
      • Valency
      • Temperature*

* temperature dependence of substitution is a result of high temperature expansion of mineral crystal lattice and the ability to accommodate greater variation in ionic radii of ions involved in the substitution.

t x phase diagrams and exsolution
At high T, lattices are more open and can accommodate cations of dissimilar size

Results in growth of a single mineral

Single mineral formed at high temp will exsolve (unmix) at lower temp

If slowly cooled

Forms two intergrown minerals

T-X Phase Diagrams and Exsolution
collaborative activity
Answer the following in groups of 2-3:

Two chemical analyses for a silicate mineral are provided.

a. Calculate the gram molecular proportions (gmp) for each sample (in the table).

b. Determine the silicate mineral group and subclass to which these samples belong.

c. Write a general formula for this mineral group

d. Determine the molecular proportions of Mg and Fe and write a chemical formula for each analysis.

Using the plagioclase feldspar T-X phase diagram:

a. On the diagram, label the liquidus and solidus

b. A liquid of composition An60 begins to crystallize. Draw the crystallization path on the diagram and determine (a) the temperature at which the first crystals form and (b) the composition of the first crystals?

c. Determine the temperature at which a plagioclase crystal of composition An40 first began to crystallize from the liquid and the composition of the liquid from which this crystal grew:

Collaborative Activity