PROPERTIES OF

MINERALS AND ROCKS

Dr. P. Sarathbabu M.Sc. B.Ed. Ph.D.

Department of Geology

Acharya Nagarjuna University

Minerals What is a mineral?

Must be solid (not made of liquid or gas).

Must be naturally occurring (not man-made).

Must be inorganically formed.

Must have an orderly internal arrangement of

atoms.

Must have a definite chemical composition

written as a formula.

• Not the same thing as minerals added to foods.

• To understand how minerals form, we need to

understand the characteristics of elements and

atoms.

• Chemical Elements

• Elements are the basic building blocks of

minerals. There are over 100 known elements.

• Atoms

• smallest particle of matter that exhibits

all the characteristics of an element.

Protons and neutrons form

the nucleus of an atom

Electrons orbit the nucleus in

discrete shells or energy levels

Physical

and chemical

properties of

minerals are

closely linked

to their atomic

structures and

compositions

The most abundant elements in Earth's crust are:

Oxygen (46.6% by weight)

Silicon (27.7% by weight)

Element Approximate

% by weight

Aluminum 8.1

Iron 5.0

Calcium 3.6

Sodium 2.8

Potassium 2.6

Magnesium 2.1

All others 1.5

All others: 1.5%

Element Abundances Silica

(SiO4)4-

SILICATES

Common cations that

bond with silica anions

Minerals are divided in to TWO types

1. Silicate Minerals

2. Non-Silicate Minerals

Silicate Minerals

• Silicates are by far the most abundant

mineral group accounting for more than

90% of the Earth's crust.

• Silicates are the major rock-forming

minerals. It follows that oxygen and

silicon are the most abundant elements

in the crust.

• The basic building block of the silicates is

the silica tetrahedron. Each silicon atom

is attached to four oxygen atoms by

tetrahedral bonds. This results in a 4-

charge on the Si04 group.

ROCK FORMING MINERAL GROUPS

a) Olivine group

b) Pyroxene group

c) Quartz group

d) Feldspar group:

e) Mica Group

f) Amphibole group

g) Garnet group

Oxides

Carbonates

Sulfides/sulfates

Phosphates

Native elements

Ferromagnesian

Silicates (Fe, Mg)

Non-Silicate Minerals

There are a few important groups of non-silicate

minerals. Only the carbonates are significant as rock-

forming minerals.

The remaining mineral groups are often ore minerals

and provide economic sources for various elements.

The important non-silicate groups are:

a) Carbonates group

b) Oxides group

c) Sulfides/Sulfates group

d) Phosphates group

e) Native elements

• Olivine

SILICATE MINERALS

dark silicates (Fe-Mg) ferromagnesian

• Pyroxene

SILICATE MINERALS

Ferromagnesian / dark silicates (Fe-Mg)

Augite

Aegirine Augite Babingtonite Enstatite

Diopside Jadeite Omphacite Spodumene

• Quartz

SILICATE MINERALS

light silicates (pure SiO2)

Rose Quartz Amethyst Milky Quartz

Chalcedony

or Cryptocrystalline Quartz Jasper Quartz in Granite

• Feldspar

SILICATE MINERALS

Orthoclase

K-feldspar

Plagioclase

Ca/Na-feldspar

light silicates (K-Na-Ca, Al)

Potassium Feldspar

(Orthoclase) Plagioclase Feldspar

in Anorthosite Labradorite

Plagioclase

in Anorthosite

Potassium Feldspar

(Microcline)

SILICATE MINERALS

Mica Group and Clay Minerals light silicates (K, Al) non-ferromagnesian

Biotite Muscovite Phlogopite

Lepidolite Phengite (Mariposite)

Margarite

SILICATE MINERALS

Amphibole Group Ferromagnesian / dark silicates (Ca, Fe-Mg)

Hornblende

Actinolite Hornblende with

Zircon and Feldspar Glaucophane

Hornblende Schist Hornblende Actinolite Closeup

• Garnet group • (R1 R2 Si3O12) where R1 can be Fe, Mg, Mn or Ca

• R2 can be Fe, Al or Cr

SILICATE MINERALS

Grossular Spessartine Uvarovite

Andradite Pyrope Almandine

NON-SILICATE MINERALS

NON-SILICATE MINERALS

• Carbonate group (Ca, mg)CO3

Aragonite Dolomite Malachite

Magnesite Siderite Cerussite

• Oxides group (Hematite and Magnetite)

Fe2O3 Fe3O4

NON_SILICATE MINERALS

Corundum Hematite Ruby (Corundum)

Magnetite Psilomelane Cuprite

• Sulphides group (Pyrite, Chalcopyrite, Galena)

FeS2 , CuFeS2 Pbs

NON_SILICATE MINERALS

Marcasite Molybdenite

Sphalerite Bornite

Pyrite

Cinnabar

• Sulfates group

NON_SILICATE MINERALS

Barite Alunite

Selenite Gypsum

Gypsum Rose

Gypsum

Halite

• Phospate group (Apatite)

• Ca2Fe(PO4)2 - 4H2O

NON_SILICATE MINERALS

Pyromorphite Variscite Turquoise

• Native elements (Diamond, Gold, Copper, Silver,

Graphite, and Platinum)

NON_SILICATE MINERALS

How do we identify minerals?

• Physical properties:

Color

Streak

Luster

Hardness

Crystal shape

Cleavage Vs. Fracture

Specific gravity

Other

Properties of Minerals

Physical Properties of Minerals

• Color:

• Most obvious, but often misleading

• Different colors may result from impurities

Example:

Quartz

Physical Properties of Minerals

Streak – color of a mineral in powdered form (used for metallic minerals)

Obtained by scratching

a mineral on a piece of

unglazed porcelain.

Example:

Hematite

Physical Properties of Minerals

• Luster:

• How a mineral surface reflects light

• Two major types:

• Metallic luster

• Non-metallic luster

Metallic

example:

Galena

Non-metallic

example:

Orthoclase

Physical Properties of Minerals

• Hardness:

• How easy it is to scratch a mineral

• Mohs Scale of Hardness

Mineral hardness is measured on a non-linear relative scale

called Mohs Scale of Hardness

• relative scale

• consists of 10 minerals, ranked 1 (softest)

to 10 (hardest)

Hardness:

HARDNESS MINERAL COMMON EXAMPLE

1 Talc Pencil lead 1.0-2.0

2 Gypsum Fingernail 2.5

3 Calcite Copper penny 3.5, brass

4 Fluorite Iron

5 Apatite Tooth enamel, knife blade, glass 5.5-6.0

6 Orthoclase Steel file 6.5

7 Quartz Scratches glass

8 Topaz ------

9 Corundum Saphire, ruby

10 Diamond Synthetic diamond

Mohs Scale of Hardness

Hardest (10) – Diamond

Softest (1) – Talc

Common objects:

- Fingernail (2.5)

- Copper penny (3.5)

- Wire nail (4.5)

- Glass (5.5)

- Streak plate (6.5)

• Crystal shape (or form):

• external expression of a mineral’s internal atomic

structure

• planar surfaces are called crystal faces

• angles between crystal faces are constant for any

particular mineral

Quartz Quartz Pyrite

Crystal System

ISOMETRIC DIAMOND

TETRAGONAL WULFENITE

HEXAGONAL BERYL

TRIGONAL QUARTZ

variety - AMETHYST

ORTHORHOMBIC TANZANITE

MONOCLINIC GYPSUM

TRICLINIC MONTEBRASITE

AMORPHOUS AMBER

• Cleavage vs. Fracture:

• The way a mineral breaks

– Cleavage: tendency of a mineral to break

along planes of weakness

– Minerals that do not exhibit cleavage are

said to fracture

Do not confuse cleavage planes with crystal faces!

Crystal faces are just on the surface and may not

repeat when the mineral is broken.

• Cleavage is described by:

• Number of planes

• Angles between adjacent planes

– These are constant for a particular mineral

• Cleavage (1 direction):

Example: mica

• Cleavage (2 directions):

orthoclase

amphibole

• Cleavage (3 directions):

halite

calcite

• Cleavage (4 directions):

fluorite

• Fracture:

• minerals that do not exhibit cleavage are said

to fracture

– smooth, curved

surfaces when

minerals break in a

glass-like manner:

conchoidal fracture

Quartz

• Specific gravity:

• weight of a mineral divided by weight of an

equal volume of water

• metallic minerals tend to have higher specific

gravity than non-metallic minerals

Galena

SG=7.5 Quartz

SG=2.67

– reaction with hydrochloric acid (calcite fizzes)

• Other properties:

– taste (halite tastes salty)

– feel (talc feels soapy, graphite feels greasy)

– magnetism (magnetite attracts a magnet)

Properties of Rocks Rock: Aggregated solids of minerals is called rock

All rocks are made of 2 or more minerals, but minerals are not made of rocks.

• There are many common names for rocks and the usually give you an idea of how big the rock is. Here are a few:

• Mountain - huge, giant hunk of rock that is still attached to the earth's crust, doesn't move, tall

• Boulder - large, taller than a person

• rock - large, you could get your arms around it or a bit smaller but it is usually jagged, broken off a bigger piece of rock

• River rock - round rocks that are along the edge & at the bottom of fast-flowing rivers

• Stone - medium, you could hold it in two hands

• Pebble - small, you can hold it with two fingers, could get stuck in your shoe, usually rounded

• Sand - made up of tiny pieces of rock, grains of sand

• Grain - tiny, like a grain of rice or smaller, often found on a beach

• Dust - really fine powder that is mixed in with sand or soil

There are three rock types

Igneous: born of fire. Form from crystallized

molten rock. Form inside earth or erupt onto

earth’s surface. Water freezing to form ice.

Metamorphic: change rock. Change produced by

heat, pressure, fluids. Takes time. NO

MELTING.

Sedimentary: composed of sediment. Clastic and

chemical sediment. Form at or near earth’s

surface.

What type of rock is formed when

magma cools and hardens?

Characteristics

A tough, frozen melt with little texture or layering;

mostly black, white and/or gray minerals; may look like

granite or like lava

What type of rock is formed

when change occurs from heat

and pressure in the Earth?

Characteristics

Hardened sediment with layers (strata) of sandy or

clayey stone; mostly brown to gray; may have

fossils and water or wind marks

What type of rock is formed when

weathering and erosion cause

sediments to press together in

layers?

Characteristics Tough rock with layers (foliation) of light and dark

minerals, often curved; various colors; often glittery

from mica

The Rock Cycle

Any rock can become any other rock through

the rock cycle.

Igneous rocks

There are 5 main kinds of igneous rocks, depending on

the mix of minerals in the rocks.

1.Granite

Grain size : Coarse grained

Usual Colour : Light (Leucocratic)

Structure : Holocrystalline

Texture : Inequi granular – equi granular

Composition : feldspar and quartz with minor

mica, amphibole or pyroxene

2. Diorite

Grain size : Coarse grained

Usual Colour : Leucocratic

Structure : Holocrystalline

Texture : Inequi granular – equi granular

Composition: low-calcium plagioclase and dark minerals

3. Gabbro

Grain size : Coarse grained

Usual Colour : Melanocratic

Structure : Holocrystalline

Texture : equigranular, hypidomorphic

Composition: contains feldspar & one or more dark mineral. The dark minerals are dominant.

4. Peridotie

Grain size : Coarse grained

Usual Colour : Melanocratic

Structure : Holocrystalline

Texture : equigranular, hypidomorphic

Composition: olivine with amphibole

and/or pyroxene

5. Pegmatite

Grain size : very coarse grained, beautiful crystal outlines

Usual Colour : Leucocratic

Structure : Holo-crystalline

Texture : inequigranular

Composition : granite with large crystals of quartz, feldspar and mica.

Dunite

Grain size : Medium grained

Usual Colour : green (mesocratic)

Structure: Holocrystalline

Texture: equigranular

Composition : at least 90% olivine

Basalt

Grain size : fine or mixed

Usual Colour : mesocratic

Composition : low-silica lava

Dolerite

Grain size : Coarse grained

Usual Colour : mesocratic

Structure: Dense, massive and compact rock

Texture: Holocrystalline, equigrannular

Composition : contains feldspars, hornblende (dark) is chief mineral, ilmenite,magnatite, qtz and biotite minerals are accessories

Metamorphic rocks are igneous or sedimentary rocks

that have been transformed by great heat or

pressure.

• Foliated metamorphic rocks have layers, or banding.

Slate is transformed shale. It splits into smooth

slabs.

Schist is the most common metamorphic rock.

Mica is the most common mineral.

Gneiss has a streaky look because of alternating

layers of minerals.

• Non-foliated metamorphic rocks are not layered.

Marble is transformed limestone.

Quartzite is very hard.

1. Slate

Grain size : fine grained

Usual Colour : Bluish black (mlno)

Structure: fine grained

Texture: fine texture

Composition :"tink" when struck

Phyllite

Grain size : fine grained

Usual Colour : shows variety of colours

Structure: schistos

Texture: fine grained

Composition : quartz, chlorite, mica,

alibite, pyrite

2. Mica

Grain size : fine grained

Usual Colour : shows variety of

colours

Structure: schistos

Texture: fine grained

Composition : quartz, chlorite, mica,

alibite, pyrite

3. Schist

Grain size : fine grained

Usual Colour : shows variety of

colours

Structure: schistos

Texture: fine grained

Composition : quartz, chlorite,

mica, alibite, pyrite

4. Gneiss

Grain size : coarse grained

Usual Colour :leucocratic

Structure: gneissos

Texture: granoblastic

Composition : feldspars mica,

Non-foliated metamorphic rocks

1. Marble

Grain size : coarse grained

Usual Colour : white, pink

Structure: coarse grained

Texture: granoblastic

Composition : calcite

Non-foliated metamorphic rocks

2. Quartzite

Grain size : coarse grained

Usual Colour : Brown

Shape: Angular

Texture: Granoblastic

Structure: coarse grained

Composition: :

Quartz,feldspars,mica and

heavy minerals

• There are 5 main kinds of sedimentary rocks depending on the appearance of the rock.

• Conglomerate rock has rounded rocks (pebbles, boulders) cemented together in a matrix.

• Sandstone is a soft stone that is made when sand grains cement together. Sometimes the sandstone is deposited in layers of different colored sand.

• Shale is clay that has been hardened and turned into rock. It often breaks apart in large flat sections.

• Limestone is a rock that contains many fossils and is made of calcium carbonate &/or microscopic shells.

• Breccia has jagged bits of rock cemented together in

Conglomerate

Grain size : coarse grained >256mm

Usual Colour : Brown

Shape: sub angular-rounded

Structure: Clastic, crude bedding

Composition : Quartz, jaspecr

Sandstone

Grain size : coarse grained

Usual Colour : Brown

Shape: subangular- subrounded

Structure: crude bedding

Composition : Quartz, feldspar

Shale

Grain size : Fine grained

Usual Colour : Yellow-black

Shape: rounded

Structure: Lamination, closed

fabric

Composition : clay minerals,

silicates

Limestone

Grain size : fine grained

Usual Colour : grey

Shape: laminate

Structure: crude bedding

Composition : calcite

Breccia

Grain size : 2mm - >256mm

Usual Colour : Reddish Brown

Shape: Angular

Structure: Clastic, crude bedding

Composition : Quartz(pebbles)

siliceous matrin chert