2 minerals

CE-312
Engineering Geology and Seismology
Lecture-2
Minerals
Instructor:
Dr. Shahid Ullah
Earthquake Engineering Center
Department of Civil Engineering, UET Peshawar.

Contents of the Lecture
 What are Minerals?
 Rocks, Ores & Gems
 Mineral Classification
 Properties and Identification of Minerals
 Common Rock Forming Minerals
2

What is Mineral?
 A naturally occuring inorganic substance which has:
• Solid at room temperature
• a more or less definite chemical composition
(representable by chemical formula), and
• definite atomic structure (ordered internal structure)
3
The mineral "halite" has a
chemical composition of NaCl.
That means it contains equal
numbers of sodium and chloride
atoms. In this case they are
electrically charged atoms, known
as ions. Those ions are arranged in
a cubic pattern that repeats in all
directions. The small sodium ions
are positioned between the larger
chloride ions

Rocks, Ores and Gems
 Rock is:
• can be an aggregate of minerals or non-minerals (organic
substance, and
• does not have a specific chemical composition.
 Ores are concentrations of minerals in rock that are high
enough to be economically extracted for use. All ores are
minerals, but all minerals are not necessarily ores. Examples
are cinnabar (HgS), sphalerite (ZnS), an ore of zinc, or
cassiterite (SnO2).
 Gems are minerals with an ornamental value, and are
distinguished from non-gems by their beauty, durability, and
usually, rarity. Examples are Diamond, Ruby, etc.
4

Rocks, Ores and Gems
5
(a)Vein gold: Vein quartz with gold
attached to basalt from California.
(a) Rock
(b)Cinnabar (Ore of Hg):Hardness:2-
2.5 . Specific gravity: ~8.1
Formula: HgS (mercury sulfide)
Crystal system: Triagonal
(b) Ore
(c)A natural, uncut octahedral diamond
crystal.Hardness: 10 (The hardest mineral)
Specific gravity: 3.6
Formula: C (Carbon)
Crystal system: Isometric
(c) Gem

Mineral Classification
 About 5000 minerals are known.
 Two major groups:
• Rockforming minerals (abundant in rocks of earthcrust)
e.g. Quartz, Feldspar etc
• Oreforming minerals (economic value, rare) e.g. Iron,
Aluminum etc
 Native Element: Minerals that are composed of
atoms from a single element are referred to as native
elements. Total 9. i.e. Arsenic (As), Gold (Au),
Silver (Ag), Copper (Cu), Diamond (C), Graphite
(C), Sulfur (S), Platinum (Pt), and Bismuth (Bi).
6

Classification of Rockforming minerals
1) Oxides: Quartz, Magnetite (Lodestone), Hematite,
Limonite
2) Carbonates: Calcite (CaC03, Polymorph of Calcium
Carbonate), Dolomite, Siderite
3) Sulphides: Pyrite, Galena, Sphalerite
4) Sulphates: Gypsum
5) Chlorides or Halides: Rocksalt
6) Silicates: Feldspars (or Felspars) ,Mica, Hornblend,
Augite, Olivine
7

1) Oxides: Minerals in which Oxygen is combined
with one or more elements. Due to abundance of
Oxygen in Earth‘s crust, very diverse in physical
properties.
• Hardness from H=9 to quite soft H=5
• Color can range from black to very colorful
8
Quartz SiO2 Hematite Fe2O3
Magnetite Fe3O4

2) Carbonates: In nature carbon atoms join with
oxygen to form carbonate ion, CO3. These ions
combine with other elements to form carbonate
minerals.
• Are transparent.
• Are lighltly-colored with a white streak.
• Soluble in acidic solutions.
9

3) Sulphides: Group of minerals that are composed of
elements with Sulphur.
• High densities
• Exhibits electrical conductivity
• Black or dark colored streak
• Are formed in igneous environments.
10

4) Sulphates: Combination of SO4 with with other
elements.
• Have average hardness
• Are, in some cases, soluble.
• Have vitreous luster.
• Are , in several cases, fluorescent.
11

5) Chlorides or Halides:
 The minerals that make up the halide
class include those in which the
halogen elements of chlorine,
bromine, fluorine, and iodine are
combined with one or more metals.
 Minerals of the halide class all:
• have relatively low hardness.
• can be transparent.
• have low specific gravities.
• have good cleavage.
• are poor conductors of heat and
electricity
12

6) Silicates: The mos common minerals, make up over
90% of the earth‘s crust. Minerals of this group are
formed by combination of SiO4 with other elements.
13
(a) Feldspars (b) Mica (c) Hornblende
(d) Augite
(e) Olivine

Properties and Identification of Minerals
 Opticial properties:The correct identification of minerals is made
with polarizing microscope.
 Physical properties are:
• Color,
• Streak,
• Lustre,
• Hardness,
• Cleavage,
• Fracture,
• Form,
• Specific gravity,
• Tenacity,
• Odor,
• Feel,
• Fluorescence,
• Phosphorescence,
• Magnetism and
• Crystal forms.
14

Color:
 Color of a mineral is that seen on its surface by
the naked eye.
 Some minerals possess a characteristic color.
e.g. The lead grey of galena, black of magnetite,
green of chlorite.
 Some minerals such as quartz and calcite have
variable color when seen in different directions. This
is called “play of color”. The reasons are:
• Isomorphous variations in compositions
• Minute colored inclusions
 The term “opalescence” is applied to minerals which
have milky appearance. e.g. Opal
 When bands of prismatic colors are seen on the
surface of a mineral, it is said to show “
iridescence”.
 Color can’t be the sole identification property. 15
galena
magnetite
chlorite
Opal

Streak:
 Streak is the color of mineral powder.
 The minerals are rubbed against unglazed porcelain
(ceramic) plate (aka. Streak plate) to observe the
color of any mark left.
 In some cases the color of the streak differs
remarkably from the color of the mineral. For
example:
• pyrite is brass yellow, but has dark green streak.
16

Lustre:
 The appearance of the mineral surface in reflected light.
 It shows the quality and intensity of light reflected from the surface
of a mineral.
 It is a measure of how shiny and smooth is the surface of a mineral.
 Various types are:
I. Metallic - strong reflection, Lustre exhibited by metal i.e. pyrite,
galena.
II. Vitreous – exhibited by the broken surface of glass, bright (shines
like glass), e.g quartz.
III. Resinous - a resin-like shine (resembling amber for example) shines
like surface is covered with oil.
IV. Greasy - a dull sheen, has the appearance of being coated with an
oily substance;
V. Pearly - a whitish iridescence (resembling pearl for example);
VI. Silky - a sheen like that of a fibrous material like silk, e.g. asbestos.
VII. Adamantine - a brilliant lustre such as that of diamond;
VIII.Dull or Earthy - like the surface of unglazed pottery
17

Hardness:
 Hardness of a mineral is its resistance to scratching.
 Is determined by comparison with the standard
minerals of the “Mohs scale of hardness”.
 Mohs scale of hardness was created by a German
geologist Friedrich Mohs in 1812.
 In this scale, 10 minerals are arranged in order of
their increasing hardness.
 A mineral can scratch minerals with low number but
not minerals with high number.
18

19
Mohs
hardness
Mineral Chemical formula Image
1 Talc Mg3Si4O10(OH)2
2 Gypsum CaSO4·2H2O
3 Calcite CaCO3
4 Fluorite CaF2
5 Apatite Ca5(PO4)3(OH−
,Cl−
,F−
)
6
Orthoclase
Feldspar
KAlSi3O8
7 Quartz SiO2
8 Topaz Al2SiO4(OH−
,F−
)2
9 Corundum Al2O3
10 Diamond C
Scratched by a finger nail
Scratched by a knife
Scarcely Scratched by a knife
Not scratched by a knife

Cleavage:
 The property of minerals to break more easily with smooth
surfaces in certain directions.
 These directions lie parallel to the actual or possible crystal
faces of the mineral, and therefore, cleavage is the property
which is related to the atomic arrangement within the mineral.
 Galena has three cleavages at right angles forming cubes.
 Mica cleaves in one direction only.
 In calcite cleavage planes meet in acute and obtuse angles giving a
rhombohedral form.
 Quartz has no cleavage.
 When minerals break with ease producing smooth lustrous
faces, they are said to have “perfect” cleave.
 Inferior degrees are described as good, distinct, indistinct, and
imperfect.
20

Fracture:
 The nature of a broken surface of a mineral, in any
direction other than the cleavage.
 Unlike cleavage, fracture does not produce smooth
planes.
 Types of fracture:
i. Uneven fracture: When the broken surface is rough or
irregular, e.g. apatite
ii. Even fracture: When the mineral breaks with a flat surface,
e.g. flint
iii. Conchoidal fracture: when the mineral breaks with curved
surfaces often with concentric markings like a shell, e.g.
Quartz
iv. Hackly fracture: when the broken surface has small sharp
irregularities like broken metal, e.g. native copper.
21

Form or habit:
 Minerals may occur either in the form of well developed crystals or they
may be massive (without development of recognizable crystals.
 crystal.: a solid substance having definte atomic structure.
 The important forms are:
– Acicular: minerals showing needle like crystal. e.g. Natrolite.
– Fibrous: minerals showing an aggregate of fibres, e.g. Asbestos
– Columnar: minerals which occur as columnar crystals , e.g. Tourmaline
– Bladed: minerals showing this form occur as small knife blades, e.g. Kyanite.
– Foliated: minerals having thin separable lamellae, e.g. Mica.
– Botryoidal: minerals showing aggregate of spheroidal masses resembling
bunch of grapes, e.g. Chalcedony.
– Reniform: minerals showing kidney shaped form, e.g. Kidney iron ore
(hermatite)
– Ganular: minerals which occur as aggregate of grains , e.g. Chromite
– Tabular: minerals showing broad flat surfaces, e.g. Feldspar
– Pisolitic: minerals which occur as aggregate of rounded grains of a pea size ,
e.g. Bauxite
– Oolitic: minerals showing an aggregate of bodies resembling fish roe. In this
case the rounded grains are of the size of a pinhead.
22

23
Form or habit:

Specific gravity:
 It is defined as the ratio of the weight of a mineral with the weight
of an equal volume of water.
 It is determined in the laboratory using the following equation:
𝑠𝑝. 𝑔𝑟 = 𝜌 =
𝑥
𝑥 − 𝑦
Whereas x is the weight of a mineral in air, and y is the wight of a
mineral in water.
 The specific gravity of a mineral is estimated as
• Low ρ 2.2 – 4.0, included silicates, carbonates, sulphates and halides
• Medium ρ 4.5 – 7.5, include metallic ores such as sulphides and oxides
• High ρ > 8.0, include native metallic elements such as pure copper, gold
and silver
24

Tenacity:
 The property of minerals which describes the behaviour of mineral
under deformation.
 It shows the degree of cohesion of a mineral amongst its elements. It
describes the physical reaction of a mineral to externally applied
stresses such as crushing, cutting, bending, and striking forces.
 Different forms are:
i. Ductile:Some minerals can be drawn out into a thin wire without
crumbling.
ii. Sectile: minerals which maybe cut with knife into slices, but slices are
not malleable.
iii. Malleable: minerals which flatten under the hammer.
iv. Flexible: minerals which maybe bent.
v. Elastic: minerals which spring back after bending.
vi. Brittle: minerals which break easily.
vii. Friable: minerals which crumble easily.
viii. Pulverulent: minerals which are powdery and have little or no cohesion.
25

Odor:
 Some minerals give characteristic smell, when rubbed, or
heated.
 Type of odor are:
• Arsenical: like the odor of garlic. e.g. Orpiment.
• Sulphurous: like the odor of burning sulphur. Pyrite gives
sulphourous odor.
• Argillacious: like odor of clay.
 Feel:
 it is the sensation of touching or handling minerals.
 The different types are: greasy, soapy, rough, and harsh.
26

Fluorescence:
 The color of minerals when exposed in sunlight or ultaraviolet
light.
 Green or colorles fluorite has a blue or purple fluorescence in
sunlight.
Phosphorescen:
• The property of mineral to glow and emit light when placed in
ultraviolet light. The glow may continue for a while after
removal of the cause.
• e.g. Diamond and sphalerite.
Magnetism:
 The property of mineral to attract to a magnet. e.g. Magnetite
and pyrrhotite. The magnetite that possesses attracting power
and polarity is called lodestone.
27

Common rock forming minerals
 The most common rock forming minerals are:
i. Feldspars
ii. Quartz
iii. Pyroxenes
iv. Amphiboles
v. Micas, and
vi. Olivine.
 They make up most of earthcrust (almost 90%)
28

Rock forming minerals
Feldspars:
 The most abundant minerals, make up as much as 60% of the
Earth's crust.
 Feldspars crystallize from magma in both intrusive and
extrusive igneous rocks, as veins, and are also found in
metamorphic rocks.
 There are two main types:
i. Orthoclase or potash feldspars contain potassium (KAlSi3O8). Found
in acid igneous rocks e.g. granites etc. Color varies from red, pink to
white.
ii. Plagioclase or soda-lime feldspars contain sodium (NaAlSi3O8),
calcium (CaAl2Si2O8) or both. Found in basic igneous rocks e.g.
basalt. Color varies from green, grey to white.
 Some properties:
• Streak: white, Luster: vitreous, Cleavage: good two sets nearly at right
angles. Hardness: 6 (moderate), Form: tabulur
29

Feldspars:
30
(a)
(b)
Orthoclase and
Plagiocalse
(a)Orthoclase
(b)Plagiocalse

Quartz:
 Second most abundant mineral in the earth’s crust,
after feldspars. Its chemical composition is SiO2 .
 There are many different varieties of quartz, several
of which are semi-precious gemstones.
 It is also very common ingredient in many kinds of
rock e.g. granite, sandstone etc.
 Properties:
• Color: Colorless or white to milywhite due to presence of
impurities, Streak: white, Luster: vitreous, Cleavage: None .
Hardness: 7 , Fracture: conchoidal
31

• Types of quartz:
32
Rock crystal (pure
quartz) colorless
Rose quartz (pink) Amethyst quartz (purple)
Smoky quartz (smokey grey)

Pyroxenes:
 They form an important group of silicates
rock forming minerals, found in basic igneous
and metamorphic rocks.
 Different types are:
i. Diopside CaMg(SiO3)2
ii. Hypersthene (MgFe)SiO3
iii. Augite (Ca, Na)(Mg, Fe, Al)(Al, Si)2 O6
 Among these, augit is the most common
mineral of the pyroxenes group. Its properties
are: Color: greenish brown or black, luster:
vitreous , cleavage: good, two sets intersects
at angle of 93 and 87, Hardness: 5-6, Form:
elongated prism
33
Greenish brown
augite
Black augite

Amphiboles:
 A group of rock forming minerals which include:
i. Tremolite (hydrous silicate of Ca and Mg)
ii. Actinolite (hydrous silicate of Ca , Mg and Fe)
iii. Hornblende (Hydrous silicate of Na, Ca, Mg, Fe and Al)
 Among these, Hornblende is the most common
amphibole. Its properties are : Color: green to black,
Luster: vitreous, hardness: 5-6, Cleavage: good, two
sets which intersects at angle of 124 and 56. Form:
elongated prism.
 Hornblende is commonly
found in igneous and metamorphic rocks.
34

Micas:
 Two common varities of Mica:
i. Muscovite (hydrous silicate of K and Al) white and
transparent,
ii. Biotite (hydrous silicate of K, Mg, Fe, and Al) or black
mica
 Their physical properties are similar: Luster: pearly,
Cleavage: perfect, Hardness: 2-3, Form: foliated
 Mica commonly occurs in granite and mica schists
etc.
35
Muscovite Biotite

Olivine:
 Is a silicate of Mg and Fe. Its chemical composition is
(MgFe)SiO4.
 It is yellowish green mineral.
 Properties are:
• Luster: vitresou, Cleavage: none, Hardness: 7, Form:
granular
 Found in ultrabasic ignesous rocks e.g. Dunite,
peridotite.
36

2 minerals

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