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