FUNDAMENTALS OF EARTH SCIENCE I

FALL SEMESTER 2018

MINERALSRock’s elementary building blocks©︎Wikipedia What is a mineral?
A mineral isRepeating unit cellNaClHalite

1. natural
2. solidNa

3. inorganic (coal is not amineral)Cl…characterized by
4. a specific chemical composition
5. a regular, repeating 3D arrangementof atoms (crystal structure)

Understanding Earth

The regular shape of crystals reflects the orderly arrangement of atoms

www.quartzpage.de

The structure of a mineral (how atoms are distributed in 3D) depends on itschemical composition, and is also a function of temperature and pressure(e.g. graphite vs. diamond).
Very high T and P

Moderate T and PDiamondGraphite Atoms, isotopes
H (1 electron)C (6 electrons)

N (7 electrons)-1-1+1-1-1-1O (8 electrons)-1-1+6-1-1-1-1+7-1-1-1-1-1+8-1-1-1-1-1-1

Electron (-)
Carbon nucleus
6 Protons (+) 6 Neutrons
Electron = negative electric charge
Proton = positive electric charge
Neutrons = no electric charge

Atoms are electrically neutralnucleusnumber of e- = number of p+

Atoms of an element with different numbers of neutrons are different
isotopes of this element.
ProtonNeutronElectron

Carbon-12 (12C)

6 neutrons
98.9 %

Oxygen-16 (16O)

8 neutrons
99.76 %

Carbon-13 (12C)

7 neutrons

Carbon-14 (14C)

8 neutrons
1.1 %

trace

Oxygen-17 (17O)

Oxygen-18 (18O)

9 neutrons
0.039 %

10 neutrons
0.201 %

Each element is characterized by its atomic number.
Atomic number = number of electrons (protons)
Atomic mass = sum of the masses of protons and neutrons
By convention, one atom of 12C has a mass of 12 amu (atomic mass unit)

The atomic mass of an element depends
on the relative abundance of its isotopes

Periodic table of elements

AtomsValency

Examples of molecules

Number of bondsthat can be formed

Optimal nbr = 8 electrons(octet rule)C

4

CH4METHANE

N

3

NH3AMMONIA

O

2

O2

FREE OGYGEN

Optimal nbr = 2 electrons

H

1

H2OWATER Chemical bonds
3 types of chemical bonds exist in minerals:
1. Covalent bond (electrons shared)
An atom shares one or more electrons with another atom, electrons
being attracted by the nucleus of each atom.
2. Ionic bon (electrons transferred)
An atom gains one or more electrons from another atom (transfer ofelectrons). The positively charged ion (cation = atom that has lost one ormore electrons) is attracted by the negatively charged ion (anion = atomthat has gained one or more electrons)
3. Metallic bond (electrons freely moving)Atoms which have a strong tendency to lose electrons (cations) are held
together by their attraction to free (mobile) electrons (“cations in a seaof electrons”).

1. Covalent bond
EXAMPLES: diamond, graphite
Each carbon atom shares 4 electrons with its
neighbors (1 with each surrounding atom of C)

Electron sharing in Diamond (2D projection)

Carbon6 e-POLYMORPHS
Carbon atoms closely packed
Each atom shares 4 electrons
with 4 other atoms

Carbon atoms arranged in sheets
Each atom shares 3 electrons
with 3 other atoms
Formed atmoderate T and P

Formed at very
high T and P

Strongbonds
Weakbonds

Strongbonds

Understanding Earth2. Ionic bond
EXAMPLE: halite (NaCl, sodium chloride, “table salt”)
The sodium atom loses one electron (cation) and the chlorine atom gains one (anion)

Cl atom
17 e-Na atom
11 e-

Na ion (+)
Cation

Cl ion (-)
Anionprimitive cell

Each Na+ is surrounded by 6 Cl-, and vice versa

Understanding Earth3. Metallic bond
EXAMPLES: gold, silver, copper, some sulfides…
Copper atom
29 eCopper mineral structure

Delocalized (free) electrons Silicate minerals
BASIC STRUCTURAL UNIT: silicon-oxygen tetrahedron = [SiO4]4- = silicate anion
Each O can share one e- with another Si (covalent bonds) or bind to a cation(ionic bonds) → possibility of combining covalent and ionic bonds
e-[SiO4]4-Oe-OSiOOe-Strong covalentbonds
SiOe-

EXAMPLES of silicate minerals

1. Quartz (SiO2)

Each Si surrounded by 4 O,and each O linked to 2 Si

Silicate tetrahedra linked by covalent bonds

SiO

www.quartzpage.de

3D structure of Quartz

Electron sharing in SiO2 (2D projection)

Combination of covalent and ionic bonds

2. Olivine [(Mg, Fe)2SiO4]
Silicate anions ([SiO4]4-) are linked to cations (Fe2+ or Mg2+) by ionic bondsFosterite:Mg2SiO4
Fayalite: Fe2SiO4Solid solution

Fe2+ or Mg2+
42+2+

The silicate anions are held together
by metallic cations (Fe2+ or Mg2+).
The -4 charge of each silicate anion
is balanced by 2 metallic cations ofcharge +2 (Fe2+ or Mg2+)

Understanding EarthSilicate sheet
Aluminium hydroxidesheet
Silicate sheet

http://www.tulane.edu/~sanelson/eens211/weathering&clayminerals.htm

 Formation of minerals

Crystallization: process by which atoms in a gas or a liquid assemble in anorderly 3D pattern (lattice) to form a solid substance (mineral crystal).
Contexts in which new minerals can form:
1. Saturation of brines – as water is removed by evaporation
and/or dissolved ions are added to the solution, the solution
becomes saturated and salt precipitate into crystals)
2. Phase change – liquid-solid, gas-solid
3. Biomineralization – biologically-induced precipitation ofminerals – biominerals – (e.g. corals, mollusks…)
4. Chemical weathering – transformation of a preexisting rockat/near Earth's surface (e.g., chemical reactions with rainwater›› 2 KAlSi3O8 + 2 H2CO3 + H2O → Al2Si2O5(OH)4 + 4 SiO2 + 2 K+ + 2 HCO3-)
5. Metamorphism – recrystallization of a preexisting rock at thesolid-state resulting from variations in T, P or in contact withhydrothermal fluids deep inside the crust.

1. Saturation of brines
1987

Major ions precipitating in the lake
are Na+, K+, Mg2+, Cl-, and SO42-.

Sebkha El Melah is a 150-km2
evaporite basin located Along
Tunisia’s southeastern coast. Sea
water rich in dissolved minerals isoccasionally discharged into the lakeand quickly evaporates once the lake
becomes isolated from the sea.

1999

Minerals formed:
NaClKCl
MgSO4.H2O…

HaliteSylviteKieserite

Landsat images (http://earthobservatory.nasa.gov)

Lake Urmia (Iran)US DEPARTMENT OF THE INTERIOR/USGS"The three rivers that supply nearly 90% of the water flowing into Urmia have all been dammed for irrigationand hydropower. And groundwater recharge to those rivers has tapered thanks to an estimated 40,000
illegal wells that have lowered the water table, Iranian experts say."
Science, Stone 2015

Calcite-aragonite
GypsumAnhydrite
HaliteSylviteBoratesNitrates

Messinian (~5.5 Ma) evaporite composed of gypsum
Source: F. Boulvain (University of Liege)

CaCO3
CaSO4.2H20
CaSO4NaClKCl
Ex: Na2B4O7·5H2O
Ex: KNO3

Messinian salinity crisis: period during which theMediterranean Sea partly or nearly completely
evaporated periodically around 5.5 Ma ago until the
Atlantic Ocean re-flooded the basin.

©︎Wikipedia

©︎Wikipedia

Garcia-Ruiz et al., 2007. Geology, vol. 35, p. 327-330

Very large crystals of gypsum (CaSO4.2H2O) precipitated out of a hydrothermal fluidsaturated in calcium and sulfate ions. A nearly stable temperature (~54ºC) and aconstant supply of calcium and sulfate ions explain the formation of these very large
crystals, which probably have been growing for more than a million years.

©︎Wikipedia

2. Phase change (e.g. solid formed by cooling of a liquid)
1.

3.

2.

Rocks formed by cooling of a magma/lava are called igneous rocks.
GENERAL PROPERTY OF CRYSTALLIZATION:
The size of crystals depends on the crystallization rate and the space
available for crystal growth.

ROCK TEXTURE AS A FUNCTION OF CRYSTALLIZATION RATE

www.geology.com

www.es.ucl.ac.uk

www.beg.utexas.edu

Slowly coolingmagma

Rapidly coolingmagma

Very rapidlycooling magma

Large crystals

Small crystals

Amorphous

BasaltVolcanic glass(no crystalline structure)

EXAMPLES: Granite

Igneous rocks are mainly composed of silicate minerals.
www.gccaz.edu

BasaltPyroxene
Plagioclase
OlivineOlivine inclusions (mantlexenoliths) in basalt
Quarz
Feldspar-K (orthoclase)
Plagioclase
Mica (biotite / muscovite)
Amphibole
Pyroxene
OlivineMica andAmphibole(black)

OlivinePyroxene

GraniteQuartz(white)Feldspar-K(pink)

SiO2
KAlSi3O8(Ca,Na)AlSi3O8
K(Mg,Fe)3AlSi3O10(OH)2 / KAl2(AlSi3O10)(OH)2
Ca2(Mg,Fe)5Si8O22(OH)2(Mg,Fe)SiO3(Mg,Fe)2SiO4

3. Biomineralization
EXAMPLE: aragonite and calcite

CaCO3
Many marine organisms produce
hard parts made of CaCO 3
Serpulid worms
Foraminifera
Molluscswww.discoverlife.org

CoralsCalcareous algae

O. R. Anderson(serc.carleton.edu)
www.physorg.com

Photo: P. Edmunds

EXAMPLE: radiolarians, diatoms

SiO2RadiolarianRadiolarite (Japan)

200 µmwww.radiolaria.org

Like foraminifers and radiolarians,
diatoms are single-celled organisms.
However, diatoms can sometimes
Diatoms form colonies of attachedindividuals.
Photo: Sarah Spaulding4. Chemical weathering

4KAlSi3O8 + 4H+ + 2H2O → 4K+ + Al4Si4O10(OH)8 + 8SiO2
Orthoclase

Hydrolysis of granite

Kaolinite

QuartzRemobilized and transported by rainwater and deposited in depressions

Kaolin quarry (Japan)
http://www.eacrh.net/ojs/index.p
hp/crossroads/article/view/14/Vo
l3_Seyock_html

NB: Kaolinite is primarily used in the paper industry (paper coating)5. Metamorphism⚫

⚫

⚫

Process by which a rock experiences at the solid state a transformation ofone or a combination of the following characteristics:◼
Chemical composition◼
Mineralogical composition◼
TextureOne or a combination of the following 3 factors are involved inmetamorphism:◼
Change in temperature◼
Change in pressure◼
Contact with hydrothermal fluids
Most metamorphic rocks form at depths of 10 to 30 km (middle to lower
half of continental crust)

SEE CHAPTER ON METAMORPHIC ROCKS Common classes of minerals

Understanding Earth

Main rock-forming minerals

Sulfides

Rich in metal sulfides and oxides (Zn, Fe, Cu, Mn)

EXAMPLES: pyrite (FeS2)
PyriteHydrothermalvents

Mid-Ocean Ridge
SeawaterS2-, Fe2+
Cu2+…

HEAT

Understanding Earth

WHOI

WHOI

Chimney of a blacksmoker rich in copperiron sulfides.

NOAA

e.g. CuFeS 2 (chalcopyrite)

Oxides and hydroxides
EXAMPLES: hematite (Fe2O3), goethite (FeO(OH)), pyrolusite (MnO2)
Important iron ore
Banded Iron Formations

Layer rich in iron oxide

Ferromanganese nodules on seafloor

www.britannica.com*JAMSTEC

Growth rate:
1 cm per million years
NOAA Physical properties of minerals
1. HARDNESS⚫

*⚫

Depends on crystal structure
Silicates with sheet structure (mica)
softer than silicates composed ofisolated tetrahedra (olivine)

Depends on chemical bonds
Harder minerals are those with:* Gypsum can be scratched by the fingernail•

Covalent bonds•

Smaller atoms/ions**•Ions with large charges•

More closely packed atoms/ions**** Control distance between opposite charges
The closer, the stronger the bonds

2. CLEAVAGE
⚫

Mica:

Chemical bond strength varies along different planes within a crystal. Acleavage defines a planar surface along which the crystal tends to split
because bonds are weaker along this surface.

Pyroxene and amphibole:

Calcite:Understanding Earth 6 th ed.

Cleavage in mica:

Understanding Earth 6thed.

3. FRACTURE⚫

Breakage that is not flat, and occurring along irregular surfaces different
from cleavage planes
Splinteryfracture(Asbestos= fibroussilicates
minerals)

Conchoidal
fracture (quartz)

www.consrv.ca.gov

4. LUSTER⚫

⚫
⚫
⚫

⚫

= the way minerals reflect light

Muscovite

Metallic (pyrite)
Vitreous (quartz)
Pearly (muscovite)
Silky (asbestos)…
www.mindat.org

5. COLOR
Citrine (quartz containing traces of Fe)◼

◼

The color of a mineral depends on how
light behaves after it reaches the surfaceof the mineral (some is reflected; some istransmitted through; some is absorbed).
It is related to the composition of themineral (including the presence of traceelements).

Debra Wilson(www.carnegiemnh.org)

Streak = color of the fine deposit left when a mineral is scraped across anabrasive surface.
Hematite (brownish red streak)Understanding Earth 6thed.

6. DENSITY
⚫

⚫

⚫

⚫

Mass per unit of volume (g/cm3)
Specific gravity: weight of a volume of a mineral divided by theweight of an equal volume of pure water at a given T and P
Examples:Pyrite (5)Calcite (2.71)
Quartz (2.65)
Halite (2.16)
Density depends on atoms' mass and atoms' packing
Increase in pressure and temperature affects mineral structure anddensity.
Example: diamond/graphite, (Mg, Fe)2SiO4 (olivine)

410 km
660 kmOlivine structure
Spinel structure
Perovskite structure
Different polymorphs of olivine stable at different depth intervals in Earth’s mantle

7. CRYSTAL HABIT⚫

Crystal habit is the shape of individual crystals.
⚫

Prism pyramidal extremity(quartz)

The crystal shape reflects
the internal arrangementof atoms/ions, and also
the speed and directionof crystal growth.

Fibrous(asbestos)Pyramidal(calcite)www.consrv.ca.gov

Cubic(pyrite)

www.mindat.org

Cubic(halite)www.mindat.org
Understanding Earth 6th

www.mindat.org