All About Minerals

• Minerals are the focus of the lecture

Luster

• This is the shine of a mineral when light reflects off its surface
• Pyrite has a metallic luster
• Quartz has a glassy luster
• Kaolinite has an earthy luster
• Muscovite has a pearly luster

Defining a Mineral

• It is naturally occurring
• An inorganic crystalline solid
• Features a definite chemical composition
• Internal atomic structure exhibits order

Non-Mineral Examples

• Synthetic diamonds
• Liquids/gases like salt water
• Organic substances like tar
• Amorphous materials like glass

Makeup of Minerals

• Minerals consist of atoms or ions of chemical elements
• Gold or silver minerals contain atoms of gold or silver
• Diamond contains carbon atoms
• Most minerals consist of ions, both cations and anions
• More than 4,700 mineral species discovered

Anions

• Oxygen (O) has a valence of -2
• Chlorine (Cl) has a valence of -1
• Fluorine (F) has a valence of -1
• Sulfur (S) has a valence of -1 or +6
• SO4 has a valence of -2
• CO3 has a valence of -2

Cations

• Silicon (Si) has a charge of +4
• Aluminum (Al) has a charge of +3
• Magnesium (Mg) has a charge of +2
• Iron (Fe) has a charge of +2 or +3
• Calcium (Ca) has a charge of +2
• Potassium (K) has a charge of +1
• Sodium (Na) has a charge of +1

Ions

• These are electrically charged atoms, having lost or gained electrons
• When an atom loses or gains an electron it is called an "ion"

Cations Defined

• Positively charged ions and lose electrons
• Calcium (Ca2+), Silicon (Si4+), and Aluminum (Al3+) are examples of cations

Anions Defined

• Negatively charged ions and gain electrons
• Oxygen (O2-) and Chlorine (Cl-) are examples of anions

Mineral Formation

• Crystallization occurs from a magma via cooling of hot molten rock
• Crystal size relies on temperature, pressure, and cooling rate
• Crystal growth happens from liquid in the solid state via cooling
• Ice crystals form below 0°C
• Precipitation from solution occurs when halite precipitates from seawater evaporation and increased NaCl saturation
• Snowflakes form from vapor
• Temperature and pressure affect a crystal's habit and density

Polymorphs

• These are two minerals sharing the same chemical composition, but differing in crystal structure
• Graphite and diamond both consist of carbon

Atomic Structure

• Atoms comprise all matter on Earth
• An atom is the smallest particle of an element
• Nucleus contains positively charged protons
• Nucleus contains neutral neutrons
• Electrons orbit the nucleus

Elements and Isotopes

• Atomic number is the number of protons in the nucleus
• Atomic number determines the element
• Oxygen has 8 protons, Iron has 26, and Carbon has 6
• Atomic mass number is the sum of protons and neutrons
• Isotopes are atoms of the same element with different atomic mass numbers

Isotopes Explained

• Isotopes are atoms of the same element
• Exhibit the same atomic number (Z)
• Feature different mass numbers (A)
• Carbon "C" has 6 protons, but can have 6, 7, or 8 neutrons
• Results in isotopes: C12, C13, and C14

Atoms Defined

• Atoms compose all matter on Earth and the natural elements
• Building blocks of minerals
• Smallest particle of an element that retains its chemical characteristics
• At the center is a nucleus containing most of the atom's mass
• Nucleus is surrounded by orbiting electrons within shells
• Nucleus consists of protons with a positive charge and neutrons with no charge
• Quarks are elementary particles forming protons and neutrons

Chemical Bonds

• These form chemical compounds when elements combine

Ionic Bond

• Involves electron transfer
• Due to electrostatic attraction
• Strong bonds
• Sodium chloride (NaCl) 

Covalent Bond

• Involves electron sharing between different elements
• Very strong bonds
• Example is diamond

Metallic Bond

• Occurs in metallic minerals
• Free electrons move through the ion network, not bound to an ionic pair
• Examples are gold and silver

Van Der Waals Bond

• Involves weak electrostatic attraction, due to off-centering of nucleus positive charges
• Very weak bonds
• Example is graphite

Silicate Minerals

• These have both ionic and covalent bonds

Ionic Bonds in Oxides

• Ionically bonded, size depends on the metallic ion involved
• Oxygen bonds to atoms or cations of other elements
• Examples of oxides include Hematite (Fe2O3)
• Corundum (Al2O3)
• Magnetite (Fe3O4)

Element Abundance on Earth

• Expressed in weight percentage

Crust Elements

• Oxygen (O): 46.3%
• Silicon (Si): 28.2%
• Aluminum (Al): 8.2%
• Iron (Fe): 5.6%
• Calcium (Ca): 4.1%
• Sodium (Na): 2.4%
• Potassium (K): 2.1%
• Magnesium (Mg): 2.3%
• Titanium (Ti): 0.5%
• Nickel (Ni): trace
• All others: trace

Whole Earth Elements

• Oxygen (O): 29.5%
• Silicon (Si): 15.2%
• Aluminum (Al): 1.1%
• Iron (Fe): 34.6%
• Calcium (Ca): 1.1%
• Sodium (Na): 0.6%
• Potassium (K): 0.1%
• Magnesium (Mg): 12.7%
• Titanium (Ti): 0.1%
• Nickel (Ni): 2.4%
• All others: 2.7%

Silicate Minerals Defined

• The most abundant mineral group on the earth's surface
• Contain SiO4 tetrahedra as their basic building block
• This forms a silica tetrahedron unit like a small pyramid
• Subdivided into crystal structure groups via arrangement of the silica tetrahedra
• Each silicon atom surrounded by four oxygen atoms
• Tetrahedra combine to make the framework of silicates
• Different combinations lead to different structures

Types of Minerals

• Minerals grouped by internal structure and chemical composition

Silicates

• The most frequent mineral group on earth
• Have SiO4 silica tetrahedron as their basic unit
• Classified into crystal structure groups based on silica tetrahedron arrangement

Isolated Silicates

• Consist of isolated silicate solids
• Olivine is an example

Chain Silicates

• Silica tetrahedra form chains
• Shared oxygen atoms
• Single chain (Pyroxene minerals) and double chain (amphibole minerals) are examples

Sheet Silicates

• Silica tetrahedra connect in two dimensions
• Form sheets like pages of paper
• Clays and micas are examples

Framework Silicates

• Silica tetrahedra connect in three dimensions
• Quartz, K-feldspar, and Na-feldspar are examples

Summary of Silicate Structures

• Isolated Silicates
• Chain Silicates
• Sheet Silicates
• Framework Silicates

Isolated Silicates Explained

• Defined as isolated solids
• Olivine with a formula of (Mg,Fe)2SiO4, is an example
• Tetrahedra are isolated from each other via cations on all sides

Chain Silicates Explained

• The silica tetrahedra form chains by sharing oxygen atoms in single or double chains
• Pyroxene [(Mg,Fe)SiO3] is an example of single chain
• Amphibole [Ca2(Mg,Fe)5Si8O22(OH)2] is an example of double chain silicate
• Single chains are linked to each other by cations
• Double chains are linked with another by shared oxygens; chains are linked by cations

Sheet Silicates Explained

• A type of silicate that involves each silica tetrahedron sharing three oxygen ions
• Results in sheets like pages of paper
• Micas such as biotite and muscovite KAl2(AlSi3O10)(OH)2

Tecto-Silicates Explained

• Silica tetrahedra are connected to each other in three dimensions
• All four oxygen are shared
• Examples are Quartz, Plagioclase, and K-Feldspar

Mafic Silicates

• High in Magnesium (Mg) and Iron (Fe) content
• Denser and darker in color

Felsic Silicates

• Rich in lighter elements like silicon, aluminum, sodium, and potassium
• Lighter in color

Mafic Minerals

• Olivine
• Pyroxene

Felsic Minerals

• Quartz (SiO2)
• Feldspars

Other Mineral Groups

• Carbonates: Minerals with one carbon atom and three oxygen atoms 
• Main carbonate is Calcite CaCO3
• Ca-carbonate
• Dolomite is another carbonate with the formula CaMg(CO3)2
• Containing Mg and Ca

Halides (Evaporites)

• Consist of evaporite minerals
• Halite (NaCl)

Sulfides

• Contain sulfur, but without oxygen
• A well-known example is Pyrite FeS2

Sulfates

• Contain sulfur and oxygen (SO4)
• Gypsum CaSO4 is the most important sulfate mineral

Oxides

• These contain only oxygen and one or more metals
• Hematite Fe2O3 and Magnetite Fe3O4 are iron oxides

Native Elements

• Consist of only one single element
• Native silver, native Gold, native copper are examples of native elements
• Native carbon is special and has two forms: graphite and diamond
• They differ in crystalline structure

Classes of Minerals

• Silicates contain silicate ion, SiO44-, for example, Quartz
• Carbonates contain carbonate ion, CO32-, for example, Calcite
• Halides contain Chloride, Cl-, Fluoride (F-), Bromide (Br-), Iodide (I-), for example, Halite
• Sulfides contain sulfide ion, S2-, for example, Pyrite
• Sulfates contain sulfate ion, SO42-, for example, Gypsum
• Oxides contain oxygen ion, O2-, for example, Hematite
• Native elements make-up of atoms, for example, Gold, Silver

Sulfides Explained

• They contain Sulfur without oxygen (S2−)
• Sulfur is an ion that gained two electrons
• Examples include Pyrite FeS2 and Galena (PbS)

Sulfates Explained

• Contain Sulfur and Oxygen (SO42−2)
• Gypsum with a formula of CaSO4·2H2O is the most important sulfate
• Hydrated version of calcium sulfate

Substitution in Minerals

• Includes elements such as Mg, Fe and Na, K which substitute each other via minor adjustment of crystal structure
• Results in a diversity of compounds
• Elements that substitute each other must be similar in size and the same charge

Simple Substitution

• Occurs when one element substitutes for another one
• For example, Olivine (Mg1Fe1SiO4 → Fe2SiO4 → Mg2SiO4), because (Fe ↔ Mg)
• Feldspar (Na Al Si3O8 → KAl Si3O8)
• Albite to Orthoclase
• Sodium ↔ Potassium

Coupled Substitution

• A couple of elements substitute for a couple of other elements.
• Observed in plagioclase (Na Al Si3O8 ↔ Ca Al2 Si2 O8)
• From Albite to Anorthite
• Sodium Silicon ↔ Calcium Aluminum

Physical Properties

• Used to identify minerals in addition to their chemical composition and structure
• Properties include Color, Crystal form, Hardness, Streak, Luster, Specific gravity, Cleavage/fracture, and other special traits

Physical Properties of Minerals

• Physical properties such as hardness, color, streak, luster, density, cleavage/fracture, and crystal form aid identification

Hardness

• Refers to a mineral's ability to resist scratching
• Specific hardness present for each mineral
• Mohs scale of hardness ranges from 1 to 10
• Talc is the softest (1)
• Diamond is the hardest (10)
• Calcite has a hardness of 3
• Quartz has a hardness of 7
• Fingernails have a hardness of about 2.5

Density

• Refers to some minerals seeming heavier than others
• Occurs even when they are of the same size or volume

Streak

• The color of a mineral in powdered form
• Rubbed against a porcelain plate

Luster

• The shine of a mineral when light reflects off its surface
• Pyrite has a metallic luster
• Quartz has a glassy luster

Cleavage vs Fracture

• Cleavage indicates a weakness where a mineral breaks easily
• Cleavage property reflects the mineral's internal crystalline structure
• Salt breaks easily into cubes
• Quartz has no preferred orientation, resulting in irregular rough fracture

Color

• Color is not that diagnostic
• Color gets affected by impurities
• Single mineral can have multiple colors

Crystal Form

• Represents an essential inherent property of a mineral
• Minerals develop particular forms; they tend to develop natural crystal faces assuming a geometric form

Physical Properties

• Color
• Crystal Form
• Luster
• Streak
• Hardness
• Cleavage

Color Explained

• Influenced by elemental substitutions, impurities, and structure defects
• Variety of colors; thus, it is not specific

Crystal Form Explained

• Essential property as crystals tend to develop natural crystal faces assuming a specific geometric form
• Needle
• Cubic
• Fibrous

Hardness Explained

• Mohs scale of hardness
• Ranked from 1-10; softest to hardest
• Fingernail (hardness of 2.5) can scratch Talc (1), and Gypsum (2)
• Copper coin scratches Calcite (3)
• A knife blade can scratch Apatite (5) and Fluorite (4)
• Window glass scratches Orthoclase (6)
• Steel file scratches Quartz (7)
• Corundum (9) scratches Topaz (8)
• Only corundum and other diamonds scratch Diamond (10)

Luster Explained

• The shine of a mineral influenced by its surface
• Gold and Pyrite have metallic luster
• Quartz has a glassy luster
• Kaolinite has an earthy luster
• Muscovite displays a pearly luster

Metallic lustre: Strong reflection produced by opaque substances Vitreous: Bright, as in glass Resinous: Characteristic of resins, such as amber Greasy: Appearance of being coated with an oily substance Pearly: White iridescence such materials as pearl Silky: The sheen of fibrous materials Adamantine: Brilliant luster of diamond and similar minerals

Streak Explained

• The color of the mineral's powder when rubbed against a porcelain plate
• Used with metallic minerals
• Hematite looks black, red, or brown will leave a reddish-brown powder trail
• Quartz is colorless (non-metallic) and has no streak.

Cleavage and Fracture Explained

• Cleavage is a plane of weakness that indicates a smooth surface
• Halite (salt) has 3 cleavage planes broken easily into cubes
• Calcite has 3 cleavage planes broken into rhombohedrons
• Muscovite has 1 cleavage plane
• Quartz has no cleavage and results in fracture

Cleavage in Silicates

• Shown in the following ways:
  • Olivine (Mg,Fe)2SiO4 exhibits 1 plane of cleavage
  • Pyroxene (Mg,Fe)SiO3 exhibits 2 planes at 90°
  • Amphibole Ca2(Mg,Fe)5Si8O22(OH)2 exhibits 2 planes at 56° and 124°
  • Mica KAl2(AlSi3O10)(OH)2 Muscovite exhibits 1 plane

Native Elements

• Examples include:
  • Silver (Ag)
  • Gold (Au)
  • Copper (Cu)