Minerals: Building Blocks of Rocks

Chapter 2

Based on: Earth Science, 10e

Minerals: the building blocks of rocks

 Definition of a mineral •  Solid •  Inorganic •  Natural •  Crystalline Structure - Possess an orderly

internal structure of atoms •  Have a definite chemical composition

 Mineraloid - lacks an orderly internal structure

Minerals: the building blocks of rocks

  Rocks are aggregates (mixtures) of minerals

•  Aggregate implies that the minerals are joined in a way that the properties of each mineral are retained

•  Some are composed of nonmineral matter

o Obsidian, pumice and coal

Composition and structure of minerals

 Elements •  Basic building blocks of minerals •  Over 100 are known

 Atoms •  Smallest particles of matter •  Have all the characteristics of an element

Periodic table of the Elements

How atoms are constructed

 Nucleus – central part of an atom that contains •  Protons – positive electrical charges •  Neutrons – neutral electrical charges

 Energy levels, or shells •  Surround nucleus •  Contain electrons – negative electrical charges

Simplified view of the atom

How atoms are constructed

 Atomic number is the number of protons in an atom's nucleus

 Isotopes •  Have varying number of neutrons •  Have different mass numbers – the sum of the neutrons

plus protons •  Many isotopes are radioactive and emit energy and

particles which power Earth’s interior movements

How atoms are

constructed

Atomic Bonding

 Bonding of atoms •  Forms a compound with two or more elements •  Ions are atoms that gain or lose electrons •  A compound is a substance consisting of two or

more elements chemically combined in specific proportions.

•  Compounds form when atoms are more stable in a combined form.

Atomic Bonding

 Types of Chemical bonds •  Ionic Bonds – form between positive and negatively

charged ions (NaCl). Rigid solids with high melting points.

•  Covalent bonds – form when atoms share electrons (SiO2 & H2O). Low melting and boiling points.

•  Metallic bonds – bonds formed when electrons are shared by metal ions. Sharing of the electron pool gives metals their characteristic properties.

Atomic Bonding

 The properties of a chemical compound are dramatically different from the properties of the elements composing it.

•  Cl green, poisonous gas

•  Na soft, silvery metal that severely reacts with water

Minerals

 How minerals form •  4 major processes by which minerals form.

o Crystallization by magma o Precipitation o Changes in pressure & temperature o Formation by hydrothermal solutions

Minerals

 Physical properties of minerals •  Crystal form - The external expression of a

mineral’s internal orderly arrangement of atoms •  Luster - Appearance or quality of light reflected

from the surface of a mineral

•  Metallic appearance of a metal

•  Nonmetallic vitreous (glassy), pearly, silky, resinous, earthy (dull)

Minerals

•  Color - An obvious, yet, unreliable property

o Slight impurities can cause a variety of colors •  Streak - Color of a mineral in its powdered

form

o A more reliable indicator of color

o Determined by using a streak plate

o Metallic minerals generally have a dense, dark streak

Minerals

 Hardness - A measure of the resistance of a mineral to abrasion or scratching

•  Mohs Scale

o Ranks minerals from 1 – 10

o Fingernail = 2.5

o Cu penny = 3.5

o Glass, Steel = 5.5

The mineral quartz often exhibits good crystal form

Pyrite (fool’s gold) displays metallic luster

Minerals  Cleavage - The tendency of a mineral to cleave,

or break, along planes of weak bonding

•  Kleiben = carve •  Not all minerals have definite planes of weak

bonding •  Those with cleavage can be identified by the

distinctive smooth surfaces that are produced when the mineral is broken

•  When minerals break evenly in more than one direction, cleavage is described by the number of planes exhibited and the angles at which they meet

Three examples of perfect cleavage – fluorite, halite,

and calcite

Minerals

 Physical properties of minerals •  Fracture - Occurs when minerals that do not

exhibit cleavage break

o Conchoidal fracture – smooth curved surfaces

o Most fracture irregularly

Conchoidal fracture

Minerals

– Specific gravity - Compares the weight of a mineral to the weight of an equal volume of water

–  “Heft”

– Usually between 2.5 & 3

– Some metallic minerals are higher

•  Galena 7.5

•  Pure 24k Gold 20

Minerals

•  Other properties •  Taste •  Smell •  Elasticity •  Malleability

Minerals

 Physical properties of minerals •  Other properties

•  Feel •  Magnetism •  Double Refraction •  Reaction to hydrochloric acid

Minerals

 A few dozen minerals are called the rock-forming minerals •  The eight elements that compose most rock-

forming minerals are oxygen (O), silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg)

•  Most abundant atoms in Earth's crust are oxygen (46.6% by weight) and silicon (27.7% by weight)

Minerals

 Mineral groups •  Rock-forming silicates

•  Most common mineral group •  Contain the silicon-oxygen tetrahedron

•  Four oxygen atoms surrounding a much smaller silicon atom

•  Combines with other atoms to form the various silicate structures

The silicate (SiO4)-4 molecule

Common silicate minerals

Minerals

 Mineral groups •  Rock-forming silicates

•  Groups based upon tetrahedral arrangement •  Olivine – independent tetrahedra •  Pyroxene group – tetrahedra are arranged in

chains •  Amphibole group – tetrahedra are arranged in

double chains

Hornblende – a member of the amphibole group

Minerals

 Mineral groups •  Rock-forming silicates

•  Groups based upon tetrahedral arrangement •  Micas – tetrahedra are arranged in sheets

•  Two types of mica are biotite (dark) and muscovite (light)

•  Feldspars - Three-dimensional network of tetrahedra

Minerals

 Mineral groups •  Rock-forming silicates

•  Groups based upon tetrahedral arrangement •  Feldspars

•  Two types of feldspar are Orthoclase and Plagioclase

•  Quartz – three-dimensional network of tetrahedra

Potassium feldspar

Plagioclase feldspar

Minerals

 Mineral groups •  Rock-forming silicates

•  Feldspars are the most plentiful mineral group •  Crystallize from molten material

•  Nonsilicate minerals •  Major groups

•  Oxides •  Sulfides

Minerals

 Mineral groups •  Nonsilicate minerals

•  Major groups •  Sulfates •  Carbonates •  “Native” elements

Native Copper

Minerals

 Mineral groups •  Nonsilicate minerals

•  Carbonates •  A major rock-forming group •  Found in the rocks limestone and marble

•  Halite and gypsum are found in sedimentary rocks •  Many have economic value

Some common non-silicate minerals

Minerals

 Mineral resources •  Reserves are already identified deposits •  Ores are useful metallic minerals that can be

mined at a profit •  Economic factors may change and influence a

resource

An underground halite (salt) mine

The Bingham copper mine in Utah

End of Chapter 1