ERTH2404 L3 Minerals Upload

7/28/2019 ERTH2404 L3 Minerals Upload

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ERTH2404

Lecture 3: Minerals

Dr. Jason Mah

Photo:C.Samson,CarletonU.


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Reading assignment

Please read Kehews book to complement the

material presented in this lecture:

Chap. 3 p. 74-94;

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Lecture contents

Mineral characteristics

Physical properties

Crystal structure

Mineral classification

Mineral identification

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What is a mineral?

Naturally occurring

Inorganic

Homogeneous solid Ordered atomic arrangement (crystal

structure)

Specific (fixed) chemical composition Almost 4000 minerals!!

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Is this a mineral?

Bone?

Seashell?

Glass? Diamond?

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Question

What is a rock?

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Answer

Rock: a solid aggregate of one or more

minerals

Minerals are the building blocks of rocks

Monomineralic: composed of one mineral Polymineralic: composed of several minerals

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Crystalline structure

Minerals have orderly internal structure

Array of atoms in a regular repeating structure

Dependent on the chemical bonds between atoms

Atom size

Crystal: the macroscopic expression of the

crystalline structure Internal structure expressed by external plane

faces

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Ionic bonds

Attraction between two oppositely charged

ions

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Covalent bonds

Sharing pairs of electrons between atoms

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Van der Waals

Weak electrostatic attraction between layers

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Crystal Structure

Atoms can be arranged in different crystal

lattice forms

Different lattice arrangement = different

mineral name

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Minerals are classified according to:

Chemical composition

Internal structure

Polymorphs:

Minerals with the same chemical composition butdifferent crystalline structures

Therefore, different properties

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Polymorphs: Carbon

16Ref.:Kehew,A.E.1998

.GeologyforEngineers&

Environmental

Scientists.2ndE

dition.Fig.2.4.Shownwithp

ermission.


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As a result of planetary differentiation:

8 elements comprise 98% of the Earths crust

Silicon and oxygen account for 75%

Inner core: Solid iron

Outer core: Liquid iron

Mantle: Iron and magnesium

Crust: Silicon and oxygen


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Composition of the crust (% weight)

Source: Earth Science Australia


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4000 minerals known

25 minerals are common

You are responsible for < 20 minerals

Mineral grouped by chemical properties


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Mineral Groups

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Group Group Formula ExampleSilicate [SiO4]

4- quartz

Oxides [O2-] magnetite

Sulfides [S

2-

] pyriteSulfates [SO4]

2- gypsum

Halides [Cl, F]1- halite

Carbonates [CO3]2- calcite

Hydroxides [OH]1- Iron ore

Phosphates [PO4]3- apatite

Native element Copper, gold


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Silicate Mineral Groups

Comprise the most rock-forming minerals

Due to abundance of Si and O in crust

1. Isolated tetrahedra

2. Single chain

3. Double chain

4. 2-dimensional sheet

5. 3-dimensional framework

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Silicate: Isolated tetrahedra

Basic building block is the silicon-oxygen

tetrahedron

Four available O ions surrounding smaller Si ion

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Silicate: Single Chains

Pyroxenese (two types)

Mg-Fe series (orthopyroxene)

Ca-Mg-Fe series (clinopyroxenes)

Together form rest of Earths mantle

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One dimensionalsingle chain

(2 free Os per ST)


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Silicate: Double Chains

Amphiboles:

Compositionally diverse:

Mg, Fe, Ca, al, Na, K, OH-

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One dimensional

double chain(2 free Os per ST)


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Silicate: 2-dimensional Sheets

Distinctly layered crystals

layers peel apart

Elements fit between sheets

Mica

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Two-dimensional

sheets


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Clay minerals

General term for a variety of complex minerals

Most originate as products of chemical

weathering

Thin stacked sheets

Sheet surface is negatively charged which attracts

water

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Clay minerals

Engineering

implications: some clay

minerals swell whenexposed to water

causing damage to

foundations

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Silicate: 3-dimensional framework

Complex structures

Most common minerals incontinental crust

Feldspars: Ca Na Ksubsitution in lattice

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Three-dimensional

sheets


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Non-Silicate Minerals: Oxides

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Oxides [O]-2 are important ore minerals

Hematite Fe2O3Magnetite Fe3O4


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Significance of Hematite

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Non-Silicates: Carbonates

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[CO3]-2

Calcite CaCO3Dolomite (Mg,Ca)CO3


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Non-Silicates: Sulfides

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Sulphides [S]-2

contain sulfur and one or moremetals

Important source of metallic ore

Sphalerite (ZnS)Galena (PbS)


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Non-Silicates: Sulfides

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Modern sulfides

found at the

seafloor of

hydrothermalvents


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Non-Silicates: Sulfates

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[SO4]-2

Gypsum (CaSO4.2H2O)


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Non-Silicates: Phosphates

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[PO4]

-3

One of very few minerals produced and used

by biological systems (bone material)

Hydroxylapatite is a major component oftooth enamel


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Non-Silicates: Halides

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[Cl,F] -

Sylvite (KCl) Halite (NaCl)


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Non-Silicates: Native elements

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Single element minerals

Sulfur


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Mineral Identification

How do we identify minerals?

Mineral identification is critical to rockidentification

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Diagnostic property

Key properties used to identify a mineral

Typically require several diagnostic properties to

identify the mineral

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Qualitative/semi-quantitative properties

1. Luster

2. Color

3. Streak4. Crystal Habit

5. Hardness

6. Cleavage

7. Fracture

8. Others

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Interaction with light

Strength

Crystal growth


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Lustre: the way that light is reflected from

mineral surface

Metallic or non-metallic?

Glassy? Greasy?

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Metallic Non-metallic


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Color

Based on visible light spectrum

Can be caused by impurities

Amethyst , violet quartz is violet due to iron

impurities

Diagnostic for some minerals, not for others

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Sulfur


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Color

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These are all the same mineral!!


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Streak

Color of the mineral in powder form

Non-metallic minerals: white

Metallic minerals: varies, but diagnostic

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Hematite - red


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Crystal habit

The crystal form of the mineral

Requires slow growth of faces

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Quartz GalenaSulfur


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Crystal habit: Twinning

Crystals grow in twins

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Growth or

Penetration TwinsStaurolite


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Twinning

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Polysynthetic Twins Plagioclase (albite twin)


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Hardness

Resistance that a smooth

surface of a mineral offers to scratching

without rupturing

Hardness is related to the strength of atomicbonds and is controlled by the weakest bond

Function of the size and the charge of ions in the

crystal structure Scale of hardness developed by Frederich Mohs

(1812): relative and non-linearscale

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Hardness

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Cleavage

Breakage of surfaces along planes of weakness

in the lattice

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Galena - cubic Amphibole - prismatic


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Fracture

Conchoidal: fracture of brittle materials that

does not follow a plane of weakness

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Quartz has

no planar

weakness


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Other: Density

Specific gravity: weight of mineral relative to

weight of equal volume of water

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Silicates: 2.5 - 3.3 Gold: 15!


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Other: Magnetism

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Pyrrhotite

(FeS)

Magnetite

(Fe3O4)

Degree to which a material is attracted by a

magnet


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Other properties

Taste (halite)

Soapy/Greasy feel (talc, graphite)

Reaction with acid (calcite)

Perthitic texture - exsolution of streaks of one

mineral inside another (K-Na feldspar;

orthopyroxene)

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Other properties

Perthitic texture in K-feldspar

Contrasting between pink and white

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Question

This mineral specimenexhibits what importantdiagnostic property of

minerals? colour

cleavage

fracture

hardness

habit

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Identifying Minerals

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Graphite

Galena

Pyrrhotite

Chalcopyrite

Pyrite

Magnetite

Ilmenite

Hematite

Chromite

Red

Brown

Black

Streak

Yes

No

MagneticGrey or

Black

Yellow or

Bronze

Yellow or

Bronze

Weakly

MagneticYes

No

Grey or

Black

Metallic

Lustre

Scratched by

fingernail

Scratched by

steel nail

Not

scratched


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Talc

Gypsum

Mica

Calcite

Halite

Fluorite

Pyroxene

Amphibole

Tourmaline

Garnet

Quartz

Non-

Metallic

Lustre

Scratched by

fingernail

Scratched by

copper coin

Scratched by

steel nail

Not

scratched

Rubs off by touch

Glassy

Thin sheets, layers

Tastes salty

Fizzes with acid

No

No

Yes

Yes

Hexagonal crystals

Square crystals

Grey Streak

White Streak

White, pink

Red

Black

Two cleavagesat 90 degrees

Glassy

Kyanite

ApatiteHexagonal crystals

Blades Blue

OlivineGreen

K Feldspar

PlagioclaseWhite

Pink


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Step 1: Metallic or non-metallic lustre?

Step 2: Verify the hardness

Does the mineral scratch your fingernail? Copper

coin? Nail? Ceramic plate?

Step 3: Verify streak, powder form of mineral

Does any other property pop out to you?


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1. Metallic or Non-Metallic lustre?

2. What is the hardness of each mineral?

3. What is the streak? Or unique property

observed?


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Carletonite

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[K,Na4Ca4Si8(CO3)4(OH,F) H2O]

Silicate mineral

Named after

Carleton Universitywhere it was firstrecognized by Prof.V. Chao

Found in only one

locality:Mont St-Hilaire,Qubec Several crystals of Carletonite. 2.8 x 2.7 cm.

Photo by John Veevaert


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