Review:

      7 mineral groups:

             Ore Minerals:

                   Carbonates; CO32-

                   Oxides;  O2-

                   Sulfides;  S2-

                   Sulfates;  SO42-

                   Halides

                   Native elements

             Rock forming Minerals

                   Silicates…We start these tonight!

 

Rock Forming Minerals

      Also known as the silicate minerals

      Core component is the Silica Tetrahedron

             1 Silicon atom

             4 Oxygen atoms

                   Si and O are Ionically bond together

                         Creates an anion with a -4 charge

                               Silicon has a +4 charge

                               Oxygen has a -2 charge

                                      1 Si = +4       4O is -8   therefore net charge is -4

 

 

 

In order to create stable compounds and structures, the tetrahedron bonds with (+) charged ions to create stable compounds

                        Or

bonds with other silica tetrahedrons covalently

 

Silicate minerals have different properties based on how the tetrahedrons join together

      Silicate minerals have cleavage along ionic bonds

      Silicate minerals have fracture along covalent bonds

 

Silicate structures

      There are 6 different silicate structures

      Each structure is different due to the way the tetrahedron bond

 

This week:

      Tonight we will look at the framework silicates.

             2 minerals:

                   Quartz 

                   Feldspar

 

 

 

Quartz

      Tetrahedrons bond with other tetrahedrons covalently

      Chemical formula is SiO2

      Covalent bonding causes quartz to have fracture…no cleavage

 

Where does quartz form?

      Found in all types of rocks.

             Igneous rocks

                   Volcanic

                   Thunder eggs

                   Magma

             Metamorphic rocks

                   veins of milk quartz

                   Recrystallization

             Sedimentary rocks

                   Cement holding seds together

                   Precipitates from supersaturated solution

 

Common Properties of Quartz

      Hardness of 7

      Some quartz can be a bit softer due to water in the structure

             Opal

                   Not a true crystal structure

                   Silica and oxygen chains are packed into spheres

                   Well ordered spheres allow light to deflect creating colors

      Fracture not cleavage

      Can be ANY color

      May not have an obvious crystal structure

 

Forms of Crystal quartz (SiO2)

      Milky quartz

             White color due to small amounts of gas or fluid

      Rock quartz

      Smoky quartz

             Grey due to exposure to radioactivity

      Blue quartz

             Inclusions of rutile or tourmaline

      Citrine

             Inclusions of iron hydrates

      Amethyst

             Ferric iron

      Rose quartz

             Manganese or titanium

      Tigers eye

             Fibers of altered crocidolite

 

      Aventurine

             Mica or goethite

      Rutilated quartz

 

Forms of microcrystalline quartz
      --Precipitated from solution
      --Low temperature formation

Agate

Jasper (iron oxides)

Onyx

Petrified wood

Carnelian (iron oxides)

Flint

Chert

 

Feldspars

      Aluminum ions can substitute for Silicon ions

             Aluminum Ions have a +3 charge where silicon has a +4 charge

             Net charge on molecule with aluminum is a -5

             Alumina substitutes for every 4th silicon

 

      Combine with cations and other silicate tetrahedrons

      Some covalent bonds between silica tetrahedron and some ionic bond with Aluminate

             tetrahedrons

 

Feldspars Composition

      Range in composition from calcium rich to potassium rich

      Which feldspar forms is temperature dependent. 

             Plagioclase feldspar (anorthite-albite) Ca-Na  rich (solid solution)

             Orthoclase feldspar (microcline) K-rich