Introduction to Minerals

Questions…

• Why learn about minerals?– They are the source of great wealth and beauty.– Minerals provide clues about the geologic past.

• How could knowing about minerals assist you in buying a home?– Some minerals are very unstable when exposed

to water and air.

• How do minerals form?

DEFINITION OF A MINERAL

•naturally occurring

•inorganic

•solid

•orderly internal structure (crystal)

•with a definite chemical composition. (can vary within a specified range)

MINERAL CLASSIFICATION

•Minerals are classified based on their:

– Physical properties –Chemical composition– Crystal Structure

ATOMIC STRUCTURE OF MATTER

•Elements–Form of matter than cannot be reduced to a simpler form by heat, cold, or chemical reactions.

•Atoms – basic form of an element.–Protons – positive charge particle in the nucleus–Neutrons – neutrally charged particle in the nucleus–Electrons – negatively charged particle outside the nucleus.

pure substances that cannot be decomposed by ordinary means to other substances.

Sodium Bromine

Aluminum

CHEMICAL ELEMENTS

Chemical Symbols

Atoms

Electron energy levels

The red compound is composed of• nickel (Ni) (silver)• carbon (C) (black)• hydrogen (H) (white) • oxygen (O) (red)• nitrogen (N) (blue)

The red compound is composed of• nickel (Ni) (silver)• carbon (C) (black)• hydrogen (H) (white) • oxygen (O) (red)• nitrogen (N) (blue)

CHEMICAL COMPOUNDS are composed of atoms and so can be decomposed to those atoms.

Compounds

– composed of 2 or more elements in a fixed ratio

– properties differ from those of individual elements

– EX: table salt (NaCl)

A MOLECULE is the smallest unit of a compound that retains the chemical characteristics of the compound.

Composition of molecules is given by

a MOLECULAR FORMULA

HH22OOCC88HH1010NN44OO22 - caffeine - caffeine

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons (All atom aspire to be “NOBLE”)

C would like to N would like toO would like to

Gain 4 electronsGain 3 electronsGain 2 electrons

1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.

2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons.

Oxygen AtomOxygen Atom Oxygen AtomOxygen Atom

Oxygen Molecule (O2)

Double and even triple bonds are commonly observed for C, N, P, O, and S

••O OC

•• ••

••

••O OC

•• ••

••

HH22COCO

SOSO33

CC22FF44

- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

Ice (water crystals) takes up more space than liquid water because of

hydrogen bonding

Metallic Bonding- electrons flow freely around metal atoms

The balance of energy

• Atoms have a desire to have their outermost energy level full of electrons, otherwise a “lone” electron may be lost to other elements or may be paired with a “lone” electron from another atom.

• Think of a teeter-totter with only one person, or one with an unbalanced number of participants.

Periodic Tablehttp://www.webelements.com/webelements/scholar/index.html

Atomic number –Number of protons and electrons

Periodic TableTendency to lose outer electrons in order to become more “stable.”

Periodic TableTendency to gain outer electrons in order to become more “stable.”

Periodic TableTransition elements – also known as the heavy metalsTend to share electrons to become stable

Periodic TableInert gases, which are already stable and don’t need additional electrons

MINERAL COMPOSITION

•Minerals are made of different ions bonded together (gain, lose, or share electrons)

•Ions are charged atoms.

Figure 2.4, Page 28

Chemical Bonding of Sodium (Na) and Chlorine (Cl)

Diagrammatic arrangement of sodium and chlorine ions in table

salt

Sharing of electrons between two chlorine ions to for a molecule of

chlorine gas (Cl2)

Stacking ions to form different crystal structures

From atomic theory to a real crystal

In Minerals (Crystals)

Physical Arrangement is more important than

Chemical Composition

BONDING IN MINERALS

•Ionic bondingopposite charges attract (gain or lose electrons)

•Covalent bonding–ions share electrons

•Metallic bonding–free moving electrons

Atomic Structure of Minerals

•Arrangement of atoms or ions in an orderly, repeating three-dimensional array.

(Gases)

Atomic Structure of Minerals

•External shape is a reflection of the internal crystal structure.

W. W. Norton

halite diamond staurolite quartz

garnet stibnite calcite kyanite

Atomic Structure of Minerals

• Polymorphism - diamond and graphite

Two Minerals from a Single ElementDiamond and Graphite

Atomic structure can lead to symmetry in some minerals

Halite

Atomic structure can lead to symmetry in

some minerals

What is the difference between a mineral and a rock?

• Rocks are made up of more than one mineral– Example: Granite contains the minerals quartz,

plagioclase, and mica.

• Minerals contain a specific chemical composition– Example: Quartz - SiO2

Growth and Destruction of Minerals

• Growth occurs through crystallization, which is the addition of atoms to a crystal face, in a liquid environment.– Requires: (1) sufficient quantity of the ions, (2)

proper temperature and pressure (space).

• Growth generally occurs in a confined space. Thus, external shape may not reflect internal structure.

ROCK-FORMING MINERALS

•Silicates

•Carbonates

•Sulfates

•Halides

Silicates

•Silica Tetrahedron–1 silicon ion bonded to 4 oxygen ions

•Silicon is positively charged (+4)

•Oxygen is negatively charged (-2)

•Net charge on tetrahedron : -4

•(SiO44-)

More details on the Silicates

• Make up 95% of the Earth’s Volume• Basic structural shape is the tetrahedron,

which defines the mineral groups:– Isolated tetrahedron (olivine)

– Single chain (pyroxene - augite)

– Double chain (amphibole)

– Two-dimensional sheet (micas, clays)

– Three-dimensional framework (quartz, feldspars)

Clay minerals

• Form at or near Earth’s surface in the presence of air and water from the breakdown of other silicates

• Sheet silicates like the micas.

• Very small crystals.

• Low density– Example: kaolinite

Isolated tetrahedron

Isolated

Isolated tetrahedron (olivine)-Does not break a certain way

Isolated tetrahedron

Single Chain

Single chain (pyroxene - augite)-Breaks on 2 planes at right angles

Isolated tetrahedron

Double Chain

Double chain (amphibole - hornblend)

-Breaks on 2 planes at 60° and 120°

Isolated tetrahedron

Two dimensional sheet

Two-dimensional sheet (micas - muscovite)

-Breaks in 1 plane

Isolated tetrahedron

Three dimensional framework

Three-dimensional framework (quartz, feldspars - orthoclase)

-Breaks on 2 planes at 90°

MINERAL IDENTIFICATION

Color Luster

Streak Cleavage

Fracture Taste

Habit Smell

Specific Gravity Magnetic

Hardness Effervescence–Mohs Hardness Scale

Bowen’s Reaction Seriesthe realationship between temperature and

the formation of crystals in magma1400 oC

800 oC

Mafic

Intermediate

Felsic

Plagioclase

Calcium-rich

Sodium-rich

Olivine

Pyroxene

Amphibole

Biotite

Orthoclase

Muscovite

Quartz

Crust composition – most common elements

Mafic

• Minerals rich in iron and magnesium

• Representative of high density, high temperature magmas.

• Examples:– Olivine, pyroxenes, amphiboles

Felsic minerals

• Minerals rich in silicon and aluminum.

• Representative of low density, low temperature magmas.

• Examples:– Feldspars, quartz, micas

Mineral Destruction

• Minerals can melt under high temperatures, removing of outer atoms - melting

• Under high pressures, some minerals melt, while others may partially melt, resulting in same chemical composition, but different crystal structure.

• Weathering - physical and chemical breakdown of minerals– Some atoms can be pried loose from the structure by

water – dissolving (example: NaCl)

Carbonates

• Basic structure contains the strong, covalent bonded carbonate ion CO3

2-

– Bonds easily (ionic) with metals, such as calcium to form calcium carbonate or calcite (CaCO3) CaCO3 is often precipitated directly from carbonate rich seawater.

– Shell organisms capture carbonate and combine it with calcium to form CaCO3.

Carbonates #2• Most common mineral is calcite and found readily in

limestone and dolomite rock.• Calcite is relatively soft, 3-4 on Mohs hardness scale, and

can dissolve in acids (even mild carbonic acid).– Results in cave formation– Weathering of statues and buildings due to acid rain.

• Calcite is one mineral that easily deforms and reforms at the Earth’s surface. Often find calcite crystals in the cracks of rocks

• Calcite can be easily mistaken for quartz, but a scratch test can remedy the dilemma.

• Dolomite (CaMg(CO3)2 bonds a little more tightly with two carbonate ions, resulting in more resistance to acid destruction.

Sulfates

• Gypsum (CaSO4 ·2H2O)

• Anhydrite (CaSO4) – note the two missing water molecules, hence the “An” in the mineral name. Plaster contains anhydrite.

• Barite (BaSO4) is soft and “greasy” feeling. Since it doesn’t burn under intense friction, barite serves as an excellent lubricant for drilling.

Halides

• Common Salt (NaCl)– Halite

• Found in thick layers where ancient seas have since evaporated.

Elements as Minerals

• Sulfur• Gold• Silver• Platinum• Diamond• Many of these metals are often associated

with sulfide minerals and low temperature silicates (e.g. quartz veins).

References

• The Mineral Gallery (commercial site)– http://mineral.galleries.com/