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Engineering Geology
ECIV 2204
Chapter (2) Minerals
Instructor : Dr. Jehad Hamad
2017-2016
Chapter 2:
Minerals:
Building Blocks of Rocks
Earth’s Molten Stage
During the early formation of the Earth it was molten
During this stage the heavier elements such as iron and
nickel, sank to the deeper interior of the Earth.
This left a thin layer of lighter materials on the surface that is
called the crust.
The majority of the Earth’s mass lies below the crust
Chemical Analysis
8 elements make up 98.6% of the crust
These 8 elements make up the solid materials of the Earth’s
crust and are known as rocks and minerals
A mineral: is solid inorganic material of the Earth that has
both a known chemical composition and a crystalline structure
that is unique to that mineral
A rock : is a solid aggregate of one or more minerals that
have been cohesively brought together by a rock-forming
process.>
(A)The percentage by weight
of the elements that make up
Earth's crust.
(B) The percentage by weight
of the elements that make up
the whole Earth.
The Earth is composed of rocks. Rocks are aggregates of minerals. So minerals are the basic building blocks of the Earth.
Currently there are over 4,000 different minerals known and dozens of new minerals are discovered each year. Our society depends on minerals as sources of metals, like Iron (Fe), Copper (Cu), Gold (Au), Silver (Ag), Zinc (Zn), Nickel (Ni), and Aluminum (Al), etc., and non-metals such as gypsum, limestone, halite, and clay. Many minerals of great economic importance and their distribution, extraction, and availability have played an important role in history.
Minerals are composed of atoms. We'll start our discussion with the geological definition of a Mineral.
Rocks and Minerals
Rocks - Mixtures of Minerals
Mixtures or aggregates of minerals are called rocks. There are three basic kinds of rocks,
each type is determined by the process by which the rock forms.
Igneous Rocks - form by solidification and crystallization from liquid rock, called magma.
Sedimentary Rocks - form by sedimentation of mineral and other rock fragments from
water, wind, or ice and can also form by chemical precipitation from water.
Metamorphic Rocks - form as a result of increasing the pressure and/or temperature on a
previously existing rock to form a new rock.
Each of these rock forming processes results in distinctive mineral assemblages and textures
in the resulting rock. Thus, the different mineral assemblages and textures give us clues to
how the rock formed. An understanding of the rock forming processes is one of the goals of
this course
Definition of a Mineral
• A mineral is Naturally formed - it forms in nature on its own (some
say without the aid of humans] ,Solid ( it cannot be a liquid or a gas)
• With a definite chemical composition (every time we see the same
mineral it has the same chemical composition that can be expressed by
a chemical formula).
• It has a characteristic crystalline structure (atoms are arranged within
the mineral in a specific ordered manner).
• Usually inorganic, although a mineral can be formed by an organic
process.
Formation of Minerals
Minerals are formed in nature by a variety of processes. Among them are:
• Crystallization from melt (igneous rocks)
• Precipitation from water (chemical sedimentary rocks, hydrothermal ore
deposits)
• Biological activity (biochemical sedimentary rocks)
• Change to more stable state - (the processes of weathering, metamorphism,
and diagenesis).
• Each process has specific temperature and pressure conditions that can be
determined from laboratory experiments. Example: graphite and diamond.
A mineral is a naturally occurring inorganic
solid possessing a definite chemical
structure that gives it a unique set of
physical properties.
Thus, ice is a mineral, but liquid water is not (since it is not solid).Halite (salt) - is naturally formed, is solid, does have a definite chemical composition that can be expressed by the formula NaCl, and does have a definite crystalline structure. So it is a minerals
Examples•Glass - can be naturally formed (volcanic glass called obsidian), is a solid, its chemical composition, however, is not always the same, and it does not have a crystalline structure. Thus, glass is not a mineral.
Ice - is naturally formed, is solid, does have a definite chemical
composition that can be expressed by the formula H2O, and does have
a definite crystalline structure when solid.
Most rocks are aggregates composed of two
or more minerals.
The building blocks of minerals are
elements.
An atom is the smallest particle of matter
that still retains the characteristics of an
element.
Each atom has a nucleus containing protons
and neutrons.
Orbiting the nucleus of an atom are
electrons.
The number of protons in an atom's nucleus
determines its atomic number and the
name of the element.
Atoms bond together to form a compound
by either gaining, losing, or sharing
electrons with another atom.
Atoms make-up minerals
An atom is the smallest component of matter
Each element is defined by the number of protons
The atom must be electrically neutral
The number of protons equals the number of electrons
AtomsSince minerals (in fact all matter) are made up of atoms, we must
first review atoms. Atoms make up the chemical elements. Each chemical element has nearly identical atoms. An atom is composed of three different particles:
•Protons -- positively charged, reside in the center of the atom called the
nucleus
•Electrons -- negatively charged, orbit in a cloud around nucleus
•Neutrons -- no charge, reside in the nucleus.
Each element has the same number of protons and the same number of
electrons.
•Number of protons = Number of electrons.
•Number of protons = atomic number.
•Number of protons + Number of neutrons = atomic weight.
Isotopes are variants of the same element
but with a different mass number (the
total number of neutrons plus protons
found in an atom's nucleus).
Some isotopes are unstable and disintegrate
naturally through a process called
radioactive decay.
Isotopes: النظائر are atoms of the same element with differing
numbers of neutrons. i.e. the number of neutrons may vary
within atoms of the same element. Some isotopes are unstable
which results in radioactivity.
•Example:
0 K (potassium) has 19 protons. Every atom of K has 19 protons.
Atomic number of K = 19. Some atoms of K have 20 neutrons,
others have 21, and others have 22. Thus atomic weight of K
can be 39, 40, or 41. 40K is radioactive.
Structure of AtomsElectrons orbit around the nucleus in different shells, A Stable electronic configuration for an atom is one 8 electrons in outer shell Thus, atoms often loose electrons or gain electrons to obtain stable configuration. Noble gases have completely filled outer shells, so they are stable.. Others like Na, K loose an electron. This causes the charge balance to become unequal. and produce charged atoms called ions. Positively charged atoms are called cations. Elements like F, Cl, O gain electrons to become negatively charged.
Negatively charged ions are called anions.
The drive to attain a stable electronic configuration in the outermost shellAlong with the fact that this sometimes produces oppositely chargedions, results in the binding of atoms together. When atoms becomeattached to one another, we say that they are bonded together.
The configuration of electrons determines if
an atom will respond with another atom
The sodium atom has one electron on its outer ring. The Chlorine atom has 7 electrons on its outer
ring. The two atoms share electrons forming an ionic bond.
Cations and Anions
The one electron on the
outer shell is given up
This leaves the sodium atom
with more protons, +1
The one electron is added to
Chlorines outer shell
This leaves the chlorine
atom with one more
electron, -1
cationanion
Types of bonding:
• Ionic Bonds - caused by the force of attraction between ions of opposite charge.
Example Na+1 and Cl-1. Bond to form NaCl (halite or salt). Ionic bonds
are moderately strong
• Covalent Bonds –• Electrons are shared between two or more atoms so that each atom has a stable electronic configuration (completely filled outermost shell) part of the time.
Example: H has one electron, needs to 2 to be stable. O has 6 electrons in its outer shell, needs 2 to be stable. So, 2 H atoms bond to 1 O to form H2O, with all atoms sharing
electrons, and each atom having a stable electronic configuration part of the time.
Covalent bonds are very strong bonds
• Metallic Bonds -- Similar to covalent bonding, except innermost electrons are also shared.
In materials that bond this way, electrons move freely from atom to atom and are constantly being shared. Materials bonded with metallic bonds are excellent conductors of electricity because the electrons can move freely through the material.
• Van der Waals Bonds -- a weak type of bond that does not share or transfer electrons.
Usually results in a zone along which the material breaks easily (cleavage). Good examples'sgraphite and micas like biotite and muscovite.
Ionic Substitution (Solid Solution)
Ionic substitution - (also called solid solution), occurs because some elements (ions) have the same size and charge, and can thus substitute for one another in a crystal structure.
Examples:
Olivines Fe2SiO4 and Mg2SiO4. Fe+2 and Mg+2 are about the same size, thus they
can substitute for one another in the crystal structure and olivine thus can have a
range of compositions expressed as the formula (Mg,Fe)2SiO4.
Composition of Minerals
The variety of minerals we see depend on the chemical elements available to form
them. In the Earth's crust the most abundant elements are as follows:
O, Oxygen 45.2% by weight
Si, Silicon 27.2%
Al, Aluminum 8.0%
Fe, Iron 5.8%
Ca, Calcium 5.1%
Mg, Magnesium 2.8%
Na, Sodium 2.3%
K, Potassium 1.7%
Ti ,Titanium 0.9%
H, Hydrogen 0.14%
Mn, Manganese 0.1%
P, Phosphorous 0.1%
Eight elements make-up 99% of the Earth’s rust
Silicon and oxygen make-up 70 % of the Earth’s crust
Note that Carbon (one of the most abundant elements in life) is not
among the top 12.
Because of the limited number of elements present in the Earth's crust
there are only about 4000 minerals known. Only about 50 of these
minerals are common. The most common minerals are those based on Si
and O: the Silicates. Silicates are based on SiO4 tetrahedron. 4 Oxygens
covalently bonded to one silicon atom
Properties of Minerals
Physical properties of minerals allow us to distinguish between minerals and thus
identify them, as you will learn in lab. Among the common properties used are:
• Habit – shape• Color
• Streak (color of fine powder of the mineral)
• Luster – metallic (reflection of light)
• Cleavage (planes along which the mineral breaks easily)
• Density (mass/volume)
• Hardness:
The properties of minerals include crystal
form, luster, color, streak, hardness,
cleavage, fracture, and specific gravity.
In addition, a number of special physical and
chemical properties (taste, smell, elasticity,
malleability, feel, magnetism, double
refraction, and chemical reaction to
hydrochloric acid) are useful in identifying
certain minerals.
Each mineral has a unique set of properties
that can be used for identification.
The eight most abundant elements found in
Earth's continental crust (oxygen, silicon,
aluminum, iron, calcium, sodium,
potassium, and magnesium) also make up
the majority of minerals.
The most common mineral group is the
silicates.
All silicate minerals have the silicon-oxygen
tetrahedron as their fundamental building
block.
In some silicate minerals the tetrahedra are
joined in chains; in others the tetrahedra
are arranged into sheets, or three-
dimensional networks.
Each silicate mineral has a structure and a
chemical composition that indicates the
conditions under which it was formed.
The nonsilicate mineral groups include:
the oxides (e.g., magnetite, mined for iron),
sulfides (e.g., sphalerite, mined for zinc),
sulfates (e.g., gypsum, used in plaster and
frequently found in sedimentary rocks),
native elements (e.g., graphite, a dry
lubricant),
halides (e.g., halite, common salt and
frequently found in sedimentary rocks),
and
carbonates (e.g., calcite, used in portland
cement and is a major constituent in two
well-known rocks: limestone and marble).
The term ore is used to denote useful metallic
minerals, like hematite (mined for iron) and
galena (mined for lead), that can be mined for
a profit, as well as some nonmetallic
minerals, such as fluorite and sulfur, that
contain useful substances.
igneoussedimentary
formed by cooling of molten
magma (lava)
formed by gradual deposition, and
in layerformed by alteration of igneous
& sedimentary rocks by
pressure/temperature
e.g., limestone, shale
e.g., marble
e.g., granite
metamorphic
Rocks formed by one of these three different processes
Clay minerals are made of two distinct structural units.
0.26 nm
oxygen hydroxyl or
oxygen
0.29 nm
Silicon tetrahedron Aluminium Octahedron
Several tetrahedrons joined together form a tetrahedral sheet.
tetrahedron
For simplicity, let’s represent silica tetrahedral sheet by:
Si
and alumina octahedral sheet by:
Al
Different combinations of tetrahedral and octahedral sheets form different clay minerals:
Different combinations of tetrahedral and octahedral sheets form different clay minerals:
Clay Mineral (e.g., montmorillonite, illite)
Si
Al
Si
Al
Si
Al
Si
Al
joined by strong H-bond
no easy separation
0.72 nm
Typically 70-100 layers
joined by oxygen sharing
Si
Al
Si
Si
Al
Si
Si
Al
Si
0.96 nm
joined by weak
van der Waal’s bond
easily separated by
water
Si
Al
Si
Si
Al
Si
Si
Al
Si
0.96 nm
joined by K+ ions
fit into the hexagonal holes in
Si-sheet
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Cation concentration drops with distance from clay particle
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Crystal Structures:
Can be made up of atoms of one or more
kinds of elements.
Crystals are classified according to six
major groups, with subdivisions of each.
A crystal is composed of a structural unit that is repeated
in three dimensions. This is the basic structural unit of a
crystal of sodium chloride, the mineral halite.
(A)The geometric shape of a
tetrahedron with four equal sides.
(B) A silicon and four oxygen
atoms are arranged in the shape
of a tetrahedron with the silicon in
the center. This is the basic
building block of all silicate
minerals.
Compare the dark colors of the ferromagnesian silicates
augite (right), hornblende (left), and biotite to the light-
colored nonferromagnesian silicates.
Compare the light colors of the nonferromagnesian silicates mica (front center), white and pink orthoclase (top and center), and quartz, to the dark-colored ferromagnesian silicates.
Structure of silicates
Isolated tetrahedrons
Chain silicates
Sheet silicates
Framework silicates
Nonsilicates – make up 8% of Earth’s crust
Carbonates
Sulfates
Oxides
Sulfides
Halides
Phosphates
Hydroxides
Native elements
Physical Properties of Minerals
Color
A visual measure.
Not very useful for identification as color of minerals varies
considerably.
Streak
This is the color of the mineral when it is finely powdered.
Rubbed across a piece of tile, leaving a fine powder of the
mineral on the tile.
Hardness
Resistance of the material to being scratched.
Measured using the Mohs hardness scale, which compares the
hardness of the mineral to 10 reference minerals.
MINERALS ARE MADE UP OF SINGLE
ELEMENTS OR COMPOUNDS
ELEMENTS A SUBSTANCE THAT CANNOT BE
BROKEN DOWN TO ANY SIMPLER
SUBSTANCE
EIGHT MOST COMMON ELEMENTS IN THE EARTH’S CRUST:
1.) OXYGEN 46% 3-8.)THE REMAINING 25% IS
COMPOSED OF Al, Fe, Ca, Na, K, Mg
2.) SILICON 29%
A MINERAL IS:
1.) NATURALLY OCCURRING
2.) DEFINITE CHEMICAL COMPOSITION
3.) INORGANIC SOLID
4.) CRYSTALLINE STRUCTURE
5.) DEFINITE SET OF CHEMICAL AND PHYSICAL
PROPERTIES
MOST MINERALS ARE COMPOSED OF TWO OR
MORE ELEMENTS
HALITE (NaCl)QUARTZ (SiO2)
• OXYGEN AND SILICON COMBINE READILY WITH EACH OTHER
AND WITH OTHER ELEMENTS TO FORM THIS FAMILY OF
MINERALS
• MOST COMMON FAMILY OF MINERALS AND MAKE UP OVER 90%
OF ALL MINERALS
• THIS IS BECAUSE OXYGEN AND SILICON ARE THE MOST
COMMON ELEMENTS IN THE EARTH’S CRUST
THE PHYSICAL PROPERTIES OF MINERALS ARE A
REFLECTION OF THE INTERNAL ARRANGEMENT OF
THEIR ATOMS Physical Properties
PhysicalProperties
LEAST USEFUL PROPERTY, CHANGE IN THE CHEMICAL
FORMULA WILL VARY THE COLOR OF THE MINERAL.
(QUARTZ) SiO2
ROSE QUARTZ
CONTAINS TITANIUM OXIDE AND MANGANESE
OXIDE TO MAKE A ROSE COLOR
CRYSTAL QUARTZ
Color
METALLIC- Looks like metal in the way the mineral reflects light
(galena or pyrite) LUSTER
- THE WAY A MINERAL SHINES IN REFLECTED LIGHT.
LUSTER
THE COLOR OF A MINERALS POWDER
RUB THE MINERAL AGAINST A
STREAK PLATE AND OBSERVE
THE POWDER’S COLOR
HOW DO YOU FIND THE
STREAK COLOR OF A
MINERAL?
Breaking Pattern:
CLEAVAGE- Tendency of a mineral to separate along planes of
weakness
ONE PLANE OF WEAKNESS
BASAL CLEAVAGE (MICA)
TWO PLANES OF CLEAVAGE AT
90* (ORTHOCLASE)
FRACTURE- NO PLANES OF WEAKNESS SO THE MINERAL BREAKS
ALONG IRREGULAR SURFACES
CONCHOIDAL- SURFACES ARE SOMEWHAT
ROUNDED, SHELL-LIKE (QUARTZ)
Resistance to be scratched; is very useful since a mineral’s
hardness is constant
• Scale to measure hardness was developed by friedrich moh in 1812
• Hardness is measured on a scale from 1 being the lowest to
10 being the highest.
• To determine the hardness of a mineral you must try to
scratch the mineral against a glass plate
Hardness