chapter 3 mineral resources

Physical Properties of Minerals• Color: Streak – color of a mineral in powdered form used for metallic minerals... Physical Properties of Minerals• Luster: – How a mineral surface refl

Matter and Minerals

Minerals: Building blocks of

• Crystal structure due

to internal arrangement of atoms

http://www.minerals.net/gemstone/index.htm

General Facts about Minerals

• Between 2 - 3,000 have been identified

• A few are “native elements” made of only one element, such as sulfur, gold copper,

and graphite (carbon)

• Most are compounds, especially the silicate group (Si, O).

• Other important groups are oxides,

carbonates, and sulfides.

Less than a dozen are common in

• Pyrite

How do we identify minerals?

Physical Properties of Minerals

• Color:

– Most obvious, but often misleading

Example:

Quartz

A mineral can be many different

colors Below is Mica.

Many minerals can be the same color Below are gold colored minerals Which

one is gold?

Physical Properties of Minerals

• Color:

Streak – color of a mineral in powdered form

(used for metallic minerals)

Pyrite or “Fool’s Gold”

• When pyrite is run

across a streak

plate, it has a black

or dark green

streak

• Pyrite is not worth

much money, while

gold is worth a lot

They look alike, so

miners call it fool’s

gold.

like it was bleeding

when it was taken

across a streak

plate

Physical Properties of Minerals

• Luster:

– How a mineral surface reflects light

– Two major types:

Orthoclase

Pyrite has metallic luster

Quartz has vitreous luster

Physical Properties of Minerals

• Hardness:

– How easy it is to scratch a mineral

– Mohs Scale of Hardness

• relative scale

• consists of 10 minerals, ranked 1 (softest)

to 10 (hardest)

Mohs Scale of Hardness

Gypsum is soft, it can be scratched by

a fingernail.

Calcite is soft, but a little harder

because it cannot be scratched by a fingernail, but it can be scratched by a

coin

Fluorite is harder It can be scratched

by a nail, but not a coin or fingernail

Diamond is the hardest mineral, so

it scratches every mineral

Physical Properties of Minerals

• Crystal shape (or form):

– external expression of a mineral’s internal

atomic structure

– angles between crystal faces are constant for

any particular mineral

Physical Properties of Minerals

• 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.

Physical Properties of Minerals

• Cleavage is described by:

– Number of planes

– Angles between adjacent planes

– These are constant for a particular mineral

Physical Properties of Minerals

• Cleavage (1 direction):

Example: mica

Physical Properties of Minerals

• Cleavage (2 directions):

orthoclase

amphibole

Physical Properties of Minerals

• Cleavage (3 directions):

halite

calcite

Physical Properties of Minerals

• Cleavage (4 directions):

fluorite

Physical Properties of Minerals

conchoidal fracture

Quartz

Physical Properties of Minerals

• 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 QuartzSG=2.67

Mineral properties

• PHYSICAL CHARACTERISTICS:

Specific Gravity S.G is an easily measured physical property that can be readily estimated In general,

sulphides and oxides have much higher specific gravities than silicates

MINERAL GROUP MINERAL SPECIFIC GRAVITY

Framework Silicate Quartz 2.6-2.7 Framework Silicate Feldspar 2.6-2.7 Sheet Silicate Mica 2.8-3.0 Chain Silicate Amphibole 2.9-3.2 Chain Silicate Pyroxene 3.2-3.6 Isolated Silicate Olivine 3.3-4.4 Isolated Silicate Garnet 3.5-4.4

– reaction with hydrochloric acid (calcite fizzes)

Physical Properties of Minerals

• Other properties:

– taste (halite tastes salty)

– feel (talc feels soapy, graphite feels greasy)

– magnetism (magnetite attracts a magnet)

• Rock-forming minerals

– ~30 common minerals make up most rocks in

Earth’s crust – Composed mainly of the 8 elements that

make up over 98% of the crust

Mineral Groups

All others: 1.5%

Element Abundances

Silica (SiO 4 ) 4-

SILICATES

Common cations that bond with silica anions

mineral formula cleavage Silicate structure Olivine (MgFe)2SiO4 none Single

tetrahedron Pyroxene (Mg, Fe) SiO3 two cleavage

group member formula uses

Fe3O4

Fe2O3

Al2O3PbS ZnS FeS2CaSO4.H2O CaSO4 Au Ag Cu S C NaCl CaF2CaCO3

Ore of iron Ore of iron Abrasive Ore of lead Ore of zinc Fool’s gold Used for plaster

Precious metal Precious metal Used for Wires Used in chemicals pencils

Common salt Used in chemicals Used in cement

Common Non Silicate mineral groups

• Silicates (most abundant)

• Non-silicates (~8% of Earth’s crust):

Mineral Groups – Silicates

• Silicates

– Tetrahedron

• fundamental building block

• 4 oxygen ions surrounding a much smaller silicon ion

Silicon-oxygen tetrahedron (SiO4) 4-

Mineral Groups – Silicates

• Joining Silicate Structures

– How tetrahedra may be linked:

Mineral Groups – Silicates –

Olivine Group

dark silicates (Fe-Mg)

Mineral Groups – Silicates

No cleavage

 ferromagnesian

The Olivine group is composed of three minerals, with the following formulas:

Forsterite = Mg2SiO4

Olivine (Chrysolite) = (Mg,Fe)2SiO4

Fayalite = Fe2SiO4

The intermediate variety, Olivine, is not scientifically

recognized as a separate mineral, but is nevertheless

mentioned

Magnesium iron silicate The series ranges from

the magnesium end member, Forsterite, through

the intermediate member, Olivine (also known as

Chrysolite), to the iron end member, Fayalite

Composition

Color Olive-green, yellow-green, light

green, yellow, yellow-brown, brown, gray, white

Crystal Forms

and Aggregates

Usually occurs as rounded

grains , in dense aggregates of

grainy crystals, and as fractured masses.

Uses The variety Peridote is a famous

gem It creates a distinctive, yellow-green to olive-green gem that is well known It is the

birthstone for August.

Olivine is also used as a flux for making steel, and is an ore of magnesium.

Pyroxene Group

Ferromagnesian / dark silicates (Fe-Mg)

Mineral Groups – Silicates

2-directions

of cleavage (at nearly 90 degrees) Augite

The typical pyroxene structure

contains chains of SiO 3

tetrahedrons

• The slope of the tetrahedral

pyramids helps to determine the cleavage angle of the pyroxenes at nearly 90 o

degrees (actually 93 o and

87 o )

Pyroxene minerals are common in in meteorites and the

extrusive igneous rock called basalt There are many

different types of pyroxene including augite, wollastonite, diopside, enstatite, and hypersthene All of the types contain

Si2O6 but some have sodium (Na) while others have iron

(Fe), magnesium (Mg), or a combination of these three

elements The general properties of the more common

pyroxene minerals, such as augite, are listed below

Shape:Orthrorhombic or Monoclinic

Luster: Glassy or metallic

Color: Black

Streak: White, light green or light brown

Hardness: 5-6.5 on Mohs hardness scale

Cleavage: Two planes that meet at nearly a 90-degree angle Fracture: Most have uneven and brittle fractures

Amphibole Group

Ferromagnesian / dark silicates (Ca, Fe-Mg)

Mineral Groups – Silicates

2-directions

of cleavage (not at 90 degrees) Hornblende

There are several different minerals within the amphibole group, but the most common type is hornblende You can find small crystals of hornblende in many types of igneous rocks They often look like little dark specks

Hornblende (Ca2Mg5)Si3O22(OH)2

Shape: Monoclinic (crystals look like short, six-sided

columns)

Luster: Glassy or milky

Color: Black or dark green, translucent to opaque

Streak: Grey-green or grey-brown

Hardness: 5-6

Cleavage: Two planes that meet at a 124-degree angle

Fracture: Uneven brittle fracture

Mica Group and Clay Minerals

light silicates (K, Al)

Mineral Groups – Silicates

1-direction

of cleavage Muscovite

 non-ferromagnesian

• Micas and Clay Minerals

• Sheets of tetrahedra are the

building blocks Aluminum

is also involved in thesesheet structures which are charge- balanced by the cations Mg,

Na and K.

• most common mica

minerals:muscovite , biotite

Mica minerals make some rocks sparkle! They are often found in

igneous rocks such as granite and metamorphic rocks such as schist They sparkle because light is reflected on their flat surfaces, which are where the mineral breaks along its plane of cleavage These minerals break so easily along their cleavage that some crystals have broken into many thin layers that look like the pages of a little book

K(MgFe)3Si3O10(OH)2

•Shape: Monoclinic

Forms flat plates

•Luster: Pearly, metallic

•Color: Dark brown, dark

green or black

•Streak: White

•Hardness: 2.5-3

•Cleavage: Yes,

•one plane of cleavage

•Fracture: The mineral is

rather flexible and so it

doesn’t fracture very

easily In fact you can

bend it very far before it

•Luster: Pearly, metallic

•Color: Colorless or lightly tinted

•Streak: White

•Hardness: 2-3 on Mohs Hardness Scale

•Cleavage: Yes, one plane of cleavage

•Fracture: This mineral is also flexible and doesn’t fracture very easily

Feldspar Group

light silicates (K-Na-Ca, Al)

Mineral Groups – Silicates

2-directions

of cleavage (at 90 degrees)

• Feldspar group

• A second group of

alumino-silicates, tetrahedra form

three-dimensional

frameworks with Ca, Na and

K as the balancing cations

• The very abundant

• feldspar are K-Na bearing

alkali

The K-feldspars or alkali felspars:

•Microcline, (Potassium aluminum

silicate)

•Orthoclase, (Potassium aluminum

silicate)

Feldspar is the most common mineral in the Earth’s crust, so you are very likely to find it in the rocks you collect! It is found it all

of the three rock types, but is most common in intrusive igneous rocks like granite where the crystals look white or pink

There are several types of feldspar The characteristics of the two most common types are listed below These two common types of feldspar are difficult to tell apart besides their color Color can be helpful, but beware because the same mineral can often have

different colors The sure way to tell these two apart is by looking

at the crystal surfaces for thin parallel groves called striations

Plagioclase feldspar has striations but orthoclase feldspar does

not

Orthoclase K AlSi 3 O 8

•Shape: Monoclinic (Flat tabular or prism-shaped crystals)

•Luster: Glassy or pearly

•Color: Cream to pink

•Luster: Glassy or pearly

•Color: White to gray

•Streak: White

•Hardness: 6-6.5

•Cleavage: perfect

•Fracture: brittle

light silicates (pure SiO2)

Mineral Groups – Silicates

no cleavage

(conchoidal fracture)

hard, resistant to weathering

Quartz

Quartz is one of the most common mineral in Earth’s crust!

Silica (Si) and Oxygen (O) are the only elements within pure quartz

Quartz can be found in all sorts of rocks Most sand is made of quartz because it is hard and does not weather away easily Some pieces of

quartz are white like milk but most are clear like glass, sometimes with a little pink or grey tinge of color

Quartz

Shape: Trigonal (Perfect crystals are usually 6-sided prisms with a

pyramid shape at the end However, it is much more common to find

many crystals that have grown in a mass or broken crystals.)

• Quartz

• Silica tetrahedra alone can

form a neutral

popular as ornamental stone and as gemstones

•Amethyst is the purple gemstone variety

•Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating

Amethyst

•Milky Quartz is the cloudy white variety

•Rock crystal is the clear variety that is also used as a gemstone

•Rosey Quartz is a pink to reddish pink variety

•Smoky quartz is the brown to gray variety

Mineral Groups

Ferromagnesian Silicates (Fe, Mg)

Non-ferromagnesian Silicates (K, Na, Ca, Al)

Oxides

Carbonates

Sulfides/sulfates

Native elements

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:

Non silicates:

• Carbonates Co3

• The important carbonates are the minerals calcite and dolomite Both are significant rock-forming minerals

• The calcite group

• Calcite (Calcium Carbonate)

Non silicates:

• Evaporites:

including the minerals halite, and fluorite;

Sulphates including the minerals gypsum and anhydrite

The most famous halide mineral, halite (NaCl) or rock salt

Non silicates:

•Gypsum:CaSO4-2(H2O), Hydrated Calcium Sulfate

Non silicates:

• Oxides

• oxides (hematite and magnetite)

Fe2O3, Iron Oxide

• hydroxides (limonite and goethite)

• important minor constituents in rocks

• aluminum oxide bauxite can also occur as a rock-forming mineral

• oxide minerals are exploited as economic sources of many elements including aluminum, antimony, iron, manganese, tin, and uranium

Non silicates:

• Sulphides

• The mineral pyrite is the only sulphide that occurs commonly in rocks

• Sulphides are most important as economic minerals providing the main sources of elements such as arsenic, copper, lead, nickel, mercury, molybdenum and zinc

• FeS2, Iron Sulfide

Non silicates:

• Sulphides

• The mineral pyrite (FeS2) is the only sulphide that occurs commonly in rocks

• Sulphides are most important as economic minerals providing the main sources of elements such as arsenic, copper, lead, nickel, mercury, molybdenum and zinc

• Galena, Chalcopyrite

Non silicates:

• Phosphates are relatively rare The only important phosphate mineral is apatite

• Ca2Fe(PO4)2 - 4H2O, Hydrated Calcium Iron Phosphate

Common minerals

• the most common minerals you'll find in rocks (rock

forming minerals)

• This pile contains plagioclase feldspar , potassium feldspar ,