Minerals are naturally occurring (not made by humans), inorganic (not from living things), solid substances (not a liquid or a gas). They have a definite chemical composition (the atoms composing the solid have an orderly, repeated pattern) and specific physical properties.
**Did you know that…? The Earth crust is made up of rocks, and rocks are made up of minerals. Oxygen is the most abundant element in the Earth’s crust. More than half the weight of a rock is made up of oxygen!
Minerals are composed of one or more chemical elements. A chemical element is a substance which is made up of only one kind of atom. An atom is the smallest particle of matter. Oxygen, hydrogen, iron and gold are examples of chemical elements. Some minerals have one single chemical element (such as gold, silver, platinum, sulphur, diamond, graphite and copper), but most are compounds: made up of more than one chemical element (Quartz, Calcite, Olivine, Biotite,…).
The chemical composition of quartz is always the same, because it is always composed of the same elements. The chemical composition of a mineral determines its physical properties.
Minerals can be found with impurities. Impurities are small amounts of other substances which are not part of the mineral. These impurities can change some of the properties of the mineral. For example, quartz is usually colourless, but it can be found in several different colours such as grey, white, pink, mauve…
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Colour.
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Shape. Minerals can be geometric or irregular.
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Lustre refers to the way minerals reflect light. They can be classified as:
metallic (like metal) or non-metallic (waxy, like oil or fat; dull or not shiny;
glassy like glass).
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Streak. The streak of a mineral is the colour of the powder left on a streak plate (a piece of unglazed porcelain) when the mineral is scraped across it.
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Cleavage is how a mineral breaks up or cleaves. For example, mica cleaves in sheets, but galena cleaves in cubes.
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Hardness measures how a mineral reacts to being scratched.
HARD: can be scratched with glass
SOFT: can be scratched with a nail
VERY SOFT: can be scratched with a fingernail
1
TALC
2
GYPSUM
3
CALCITE
4
FLUORITE
MOHS SCALE OF HARDNESS
VERY HARD: can scratch glass
5
APATITE
6
ORTHOCLASE
7
QUARTZ
8
TOPAZ
9
CORUNDUM
10
DIAMOND

Minerals are used in everyday life.
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At home: Fluorite is used in the composition of toothpaste. You must use talc after your shower. The salt you put on your food is the mineral Halite.
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At school: Your pencil is made of graphite. Your digital watch can be made using quartz, aluminium, gold or silver.
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In the shops: Gold, silver and platinum are used to make jewellery. Precious stones are minerals: diamonds, sapphires and amethysts. Your dentist sometimes uses gold to fill teeth.
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Construction materials: Plaster is made from talc. Cement is made from
calcite. Glass is made from quartz.
ACTIVITIES
I.
II.
…
Are the following minerals? Answer using the table. Mercury, pyrite, amber, gold, water, diamond, animal bone, plastic,
Is
Is not a mineral because it is it is not natural. inorganic. solid.
Research some varieties of quartz. What colours are they? a.
Amethyst. b.
Jasper. c.
Smocky quartz. d.
Citrine. e.
Creolite.
III.
f.
Rose quartz. g.
Rock crystal. h.
Agate.
Study the Mohs Scale of hardness and describe each mineral.
Talc is harder than softer than apatite.
IV.
Work in pairs. Describe your test for hardness.
Rocks are any natural material made up of a mixture of minerals.
Some rocks are made of a single substance. They are called monomineralic rocks, like limestone (calcite), salt (halite), quartzite (quartz), gypsum.

Some rocks, such as coal and oil, aren’t made of minerals but of the remains of living things. Others can be found in liquid form, for example, oil.
The scientific study of rocks is called petrology. People who study rocks are called
geologists.
How are rocks classified?
Rocks are divided into three main classes according to their origin (how they were formed): sedimentary, igneous and metamorphic.
Sedimentary rocks are formed by the accumulation and compaction of sediment.
They are classified into three groups: detrital, chemical and organic.
Detrital rocks are made up of fragments of other rocks that are stuck together.
Chemical sedimentary rocks are made of mineral crystals from oceans, lakes and groundwater that have dissolved in water.
Organic sedimentary rocks are made of plant and animal remains which have been transformed into “minerals”.
Sedimentary rocks can contain fossils (remains of living things that lived millions of years ago.
Fragments of rock and some sand
Small grains of sand
Very small grains
Chemical reactions.
All contain calcium carbonate.
Evaporation of the water in deposits
Round or angular fragments
Grains break off if scratched
Different colours.
Smells like wet earth when wet
Reacts to acids by producing bubbles
Very soft. Can be scratched with a fingernail
Tastes salty
Remains of land vegetation
Remains of marine plants and animals
Soft, black. Burns easily
Thick, black liquid
Igneous rocks are formed as a result of the cooling and solidification of magma.
Magma is the melted, rocky material from below the Earth’s crust or mantle. Magma consists of silicates, water and gases at high temperature. Lava is magma without gases on the Earth’s surface.
There are two types of igneous rocks:

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Plutonic (intrusive) rocks form as magma cools down slowly inside the Earth, over thousands of years. As a result, the mineral crystals are large.
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Volcanic (extrusive) rocks form as lava cools down rapidly on the surface of the Earth. As a result, the mineral crystals are tiny.
Granite
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Made up of quartz, feldspars and mica
Large, visible crystals
The most common rock in the continental crust
Many colours- pink to grey and black
Very hard and strong
Basalt
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Dark or black colour

Heavy and hard
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It may contain olivine crystals
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It may have a few bubble holes
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The most common rock on the ocean floors
Pumice
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Mostly light colours
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Light weight and floats in water
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Spongy texture from bubble holes
Obsidian
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Black and smooth
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Looks like black glass
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The edges can cut
Metamorphic rocks are formed deep within the Earth by the effects of intense heat and pressure on sedimentary, igneous or other metamorphic rocks. They rarely have fossils.
Common
Metamorphic rocks
Slate
Appearance
Usually black, slightly shiny because of the presence of mica
Properties
Hard, but can be separated into thin layers or sheets
(foliation)
Marble
Many different colours. Often with veins
Does not separate into layers. Marble reacts with acids, such as vinegar or hydrochloric acid, producing CO
2 bubbles