this is how we classify minerals! silicates and...
Post on 31-May-2020
6 Views
Preview:
TRANSCRIPT
Why are some minerals harder than others?
Their atomic structure and chemical formula.
This is how we classify minerals!Silicates and Non-Silicates
Part #1 - Silicates:
• Silicon and Oxygen make up 70% of the earth’s crust and are therefore the two most common elements.
• The largest group of minerals, therefore, is the SILICATE GROUP: all of which are compounds containing silicon and oxygen along with various other elements.
Percentages of Elements in Earth's Crust
Silica Tetrahedron:• Tetrahedron: The basic unit of all
silicates.
• Formed by ONE Silicon Atom surrounded by FOUR Oxygen Atoms.
• Shaped Like a Pyramid
Silicon
Oxygen 4
1
• The Silicates are subdivided on basis of crystal structure:
• In other words…the ways in which the Silicon-Oxygen Tetrahedra are linked together!
STRUCTURAL GROUPING OF THE SILICATE MINERALS: BASED ON HOW SILICON-OXYGEN TETRAHEDRA ARE ARRANGED!
FrameWork Silicates - (Basically a 3D tightly packed mass of
Tetrahedra) Tend to be very HARD & resistant to
weathering!!
Feldspars***
Most Common Mineral On Earth!! Compose About 60% of the Earth’s Crust
Quartz** Second Most Common Mineral On Earth!!
Sheets -Micas*
Biotite = Brown Muscovite = White
ChloritesClays
Chains Of Tetrahedra -Pyroxene = Single Chain
AKA “Augite”
Amphibole = Double Chain
AKA “Hornblende”
Isolated Tetrahedra - OlivineGarnet
Increasing Structural Complexity
Isolated Tetrahedra:• The simplest arrangement of Tetrahedra.
• OLIVINE & GARNET.
• Ionic bonding with Magnesium or Iron
• Glassy looking, pale green
• Found in oceanic crust and upper mantle
Olivine
• Another common single tetrahedron silicate is GARNET.
• SiO4 tetrahedrons bonded to Magnesium, Iron, Calcium, or Manganese.
• Reddy brown to black in colour.
• Found in continental crust.
• Commonly form crystals
CHAIN SILICATES:
• Other silicates have their Tetrahedra arranged in chains.
• Formed by the sharing of Oxygen atoms between adjacent Tetrahedra in one dimension.
• Two Types - single chains and double chains
Single chain structure in pyroxenes
Double chain structure in amphiboles
Single-chain Silicates-• One large group of single-chain silicates is
collectively known as PYROXENES.
• PYROXENE is also called AUGITE
• Ionic bonding of SiO4 tetrahedrons with Calcium and Magnesium single chains.
• Shiny black in color, and luster
• Found in oceanic crust and mantle
Double-chain silicates-
• Known as AMPHIBOLES.
• A common AMPHIBOLE is HORNBLENDE:
(Ca,Na)3(Mg,Fe,Al,Ti)5(Si,Al)8O22(OH,F)2
• Ionic bonding of SiO4 tetrahedrons with Calcium, Magnesium, and Hydroxides
• Dark green to black in color
Sheet Silicates:• Tetrahedra are linked by shared Oxygen
atoms in 2 dimensions.
• MICAS are a compositionally diverse group of sheet silicates that have in common excellent cleavage parallel to weakly bonded sheets of Tetrahedra
Sheet Arrangement of Tetrahedra
• MICAS: –MUSCOTIVE often found in granite,
colorless (clear) – BIOTITE rich in iron and magnesium giving
it a dark brown-black color
• CHLORITE: usually green in color
• CLAY MINERALS are also sheet silicates and their slippery feeling can be attributed to the sliding apart of such sheets of atoms – Earthly smell
– Example: Kaolinite, which is white in color
Framework Silicates:
• Tetrahedra are firmly linked in all 3 dimensions by shared Oxygen atoms.
• Basically a tightly packed mass of Tetrahedra.
• Tend to be very HARD and resistant to weathering & therefore VERY COMMON!!
Feldspars:
• Most common mineral on earth!!
• 60% of Earth’s crust...
• Two types:
– Potassium Feldspar or K-SPAR or Orthoclase – Contains “K” potassium. – Pinkish in colour
– Plagioclase: – traces of sodium, calcium, or both in their structure – Whitish in colour
Quartz:
• Second most common mineral on Earth.
• Framework exists entirely of Silicon-Oxygen Tetrahedra, the net charge on each is 0.
• 0 impurities.
• Only mineral to exhibit this type of structure.
• Found extensively in continental crust
• Colour can vary from white to black
Silicates Summary:• ISOLATED TETRAHEDRA
– Olivine – Garnet
• CHAIN SILICATES – Pyroxene (Augite) (SINGLE) – Amphibole (Hornblende) (DOUBLE)
• SHEETS – Micas – Clays – Chlorites
• FRAMEWORK SILICATES – Feldspars (most common, 60% of Earth’s crust) – Quartz (second most common mineral)
Part #2 - Nonsilicates:
• Each Nonsilicate Mineral group is defined by some chemical characteristic that all members of the group have in common.
NONSILICATES:
1. Carbonates 2. Halides 3. Native elements 4. Oxides 5. Sulfides 6. Sulfates
CARBONATES:• Chemical formulas all contain the Carbonate
Group (CO3) • Are not made of SiO4 Tetrahedra! • Not as common as silicate minerals but usually
more valuable economically • Carbonate minerals dissolve easily, particularly in acids…said to Effervesce!
• Oceans contain a great deal of dissolved carbonate
• Most important carbonate mineral is CALCITE (CaCO3)
• DOLOMITE is another common carbonate mineral
– Contains calcium and magnesium (CaMg(CO3)2)
HALIDES:• Structure includes chlorine or fluorine
combined with sodium, potassium or calcium
• Example: Fluorite (CaF2) or Halite (NaCl)
Fluorite
NATIVE ELEMENTS:• Minerals that are each made up of a single
chemical element.
• Structure is a pure substance of only one element.
• Minerals name is usually same as names of corresponding elements.
• Ex) Gold, Silver, Platinum, Copper, Sulfur Etc.
• Ex) Diamond and Graphite are both examples of native carbon
Native gold
Native silver
Native Copper
OXIDES:• Minerals that contain just
one or more metals combined with oxygen and that lack the other elements necessary for them to be classified as silicates, sulfates, carbonates, etc.
• Structure includes oxygen and anther element which cannot be silicon
• Magnetite (Fe3O4) • Corundum (Al2O3) • Hematite (Fe2O3)
SULFIDES:
• When sulfur is present without oxygen.
• Usually heavy dense metallic minerals.
Examples:
Iron sulfide = PYRITE (FeS2) Also called “fool’s gold” Metallic golden color
Lead sulfide = GALENA (PbS) Forms in silver colored cubes
Zinc Sulfide = SPHALERITE (ZnS)
Pyrite
Sphalerite
SULFATES:• All contain the Sulfate Group (SO4). sulfur WITH oxygen!
• The calcium sulfate GYPSUM is most important – Abundant – Commercially useful
• Sulfates of other elements are also found: barium, lead, strontium for example.
Nonsilicates Summary:
• CARBONATES – Carbonate group (CO3)
• Calcite, dolomite
• HALIDES – Chlorine/fluorine combined with sodium, potassium or calcium
• Halite, fluorite
• NATIVE ELEMENTS – Pure substance of one element
• Gold, silver, copper
• OXIDES – Oxygen and another element which cannot be silicon
• Magnetite, corundum, hematite
• SULFIDES – One or more elements combined with sulfur
• Sphalerite, pyrite, galena
• SULFATES – Sulfate group (SO4)
• Gypsum
top related