3
The Geosphere
110
2.1.2.
Mechanical properties
Ask students to read the text and look at the table illustrating
Mohs Scale.
Ask the students to re-read the text and identify three mechanical
properties (hardness, cleavage, tenacity). Then ask them what the
other properties are: magnetic (not all minerals), transparency and
density.
Students should now do questions 12 to 14.
Tips: For question 12, ask the students to look at the scale
in pairs, and to decide not only what it is measuring but why
this would be useful: Brainstorm ideas on the board. For
question 13, do this activity quickly with the whole class, then
ask students to think of other quiz-type questions to identify
another property.
For question 14, play the audio at least twice. The second time,
stop after each sentence and elicit the answer.
Now ask students to do questions 15 and 16. They can do this
as homework, or if they access to reference material (digital or
otherwise), they could do it in class. Ask them to discuss their
findings before handing in their report.
2.2.
The importance of minerals
Once students internalise the definition and the properties
of minerals, it should be easier for them to understand their
importance and the sustainable management of mineral
resources.
Video:
A DAY WITHOUT MINERALS
This video shows some daily objects that are manufactured with
minerals. After watching the video twice, ask the students to
answer the questions given in the worksheet. To finish the activity,
ask students: What do we use minerals for nowadays?
Finish the section revising the Key concepts at the end of
the section and also remind them about the Final task that
they should do about the environmental impact of mineral
extraction.
Curricular adaptation:
3. PROPERTIES OF MINERALS
Section adapted according to the curriculum.
Answer key
Remember
12.
Explain in your own words what the Mohs scale is?
What is it used for?
It is a scale that measures the hardness of minerals. Hardness
is not a quantitative property so that is the reason the Mohs
scale is so useful to classify minerals and their uses.
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3. Thegeosphere
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2.1.2.
Mechanical properties
❚
Hardness describes a mineral’s
resistance to scratching. To check if
a mineral is harder than another, we
can scratch one with the other. The
mineral that is scratched is softer than
the mineral that scratches it.
Wecanuseminerals thatare listedon
the
Mohs scale
to identify hardness.
This scale grades the hardness of 10
minerals from 1 to 10. The softest
mineral, Talc (1) can be scratched by
all the others. At the other end of the
scale, diamond (10) can scratch all
the other minerals and can only be
scratched by another diamond.
❚
Cleavage
describes the way a mineral breaks. Many minerals break to show flat
surfaces, maintaining the crystalline structure. For example, galena breaks into
cubic shapes and gypsum breaks into sheets.
❚
Tenacity
describes how easily a mineral breaks. A fragile mineral breaks easily,
such as talc.
Some minerals can be pulled into thin threads. This is the case of copper threads
that conduct electricity. This is called
ductile
tenacity.
2.1.3.
Magnetic properties
Some minerals, such as
magnetite
, behave like a magnet. They attract objects
that contain iron and nickel.
2.1.4.
Other properties of materials
❚
Transparency
describes how a mineral reacts to light. A mineral can be
transparent
, such as diamond, when light can pass through it;
translucent
,
like quartz, when light passes through it but is distorted; or
opaque
, like
galena, when no light can pass through.
❚
Density
is the relation between the mass and volume of a mineral (density
= mass/volume). Density is usually measured in grams per cubic centimetre
(g/cm
3
). This property is specific to each mineral and is independent of size.
So, the density of a mineral is important information for identifying minerals.
Gypsum
Magnetite
2.2.
The importance of minerals
Throughout history, the ability to identify minerals and to obtain raw materials has
been essential to the success of civilizations.
Today,mineralsareusedmainlyasmetal
ores
,as rawmaterials for industry,or sold
as gems or precious stones.
2.2.1.
Metal ores
These are minerals that metals are extracted from (see table on the right). Other
minerals known as
native
or
noble minerals
are found in nature in their pure
state.Examplesof thesemineralsaregold, silverorplatinum,admired sinceancient
times for their colour, beauty, easiness to mould and durability.
2.2.2.
Raw materials for industry
Thesearethemostabundantmineralsfound intheEarth’scrust.Someexamplesare:
uraninite
which provides us with uranium used as fuel in nuclear power stations;
quartz
, which is very important for manufacturing glass, computer components,
parts and solar panels; and
gypsum
, which is used for manufacturing plaster,
alabaster, fertilisers and explosives.
2.2.3.
Gems or precious stones
These are beautiful and rare minerals which have a great economic value. They are
used for jewellery,usuallyafteraprocessofcuttingandpolishing tobringout their
lustre.Someof themostwell-knowngemsare
diamonds
,
rubies
,
sapphires
and
emeralds
.
2.3.
Sustainable management of mineral resources
Uncontrolled mining has an impact on the environment such as contamination of
water and land contamination with metals. It can also cause health problems for
miners:headaches,bloodpoisoningwith leadandmercury,andbreathingproblems.
Responsibleuseofminerals isessential toavoidor reduce thisnegative impact.We
can help by recycling minerals and electronic devices made with minerals such as
mobile phones and computers.
Diamond
Ruby
Sapphire
Emerald
Mainoresof somemetals
Ore
Metal
Bauxite
Aluminium
Blende
Zinc
Chalcopyrite Tin
Cinnabar
Mercury
Galena
Lead
Hematite
Iron
Key concepts
❚
Minerals are solid, inorganic
substances of natural origin.
They have a definite chemical
compositionandmosthavea
crystallinestructure.
❚
They have properties that
allow us to identify them
such as hardness, lustre,
streak or density.
❚
Theyareusedasmetalores,
as raw materials for industry
and as gems or precious
stones.
Mohs scale
Hardness
Mineral
Characteristics
1
Talc
Very soft, because it can be scratched by another
mineral.
2
Gypsum
3
Calcite
Soft minerals that can be scratched by the point of
a knife.
4
Fluorite
5
Apatite
6
Orthoclase Hard minerals. Orthoclase can be scratched with
sandpaper and quartz scratches glass.
7
Quartz
8
Topaz
Very hard, cannot be scratched by any other
mineral.
9
Corundum
10
Diamond
Galena
Quartz
The
mechanical properties
of minerals refer to how the mineral behaves
when a force is applied to its surface.
Understand
12.
Explain in your own words what the Mohs scale is? What is it used for?
13.
A crystal is hit and breaks into small cubes. What property does this describe?
Analyse
14.
Listen and say which mineral properties are being described.
Analyse
15.
Find out about the use of the metals extracted from these mineral
ores: bauxite and cinnabar. Write a short report in your notebook.
16.
Findoutabout thehardnessof thegems in thephotos above. Doyou
think their economic value is related to their hardness? Explain your
answer.
