Elements and compounds found naturally in the earth.
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What main properties help us to identify minerals?
Colour, cleavage/fracture, hardness, density, streak, lustre and reaction with acid.
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How do you work out relative density?
Density= mass / volume
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How do you use streak?
Scrape the mineral along an unglazed white tile, a power is produced. We use this by using the colour of the powder.
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What does cleavage mean?
The ability of a mineral to break along planes of weakness- this is caused by weak bonds between atoms.
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What happens when a mineral has one set of cleavage planes?
The mineral splits into thin sheets. An example of this is mica.
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What happens when a mineral has two sets of cleavage planes at right angles?
The mineral splits into needles with a square cross section. An example of this is pyroxene.
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What mineral has two cleavage planes with a 60 degree angle between them?
Amphibole. The cross section of the needle is diamond shaped.
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What happens when a mineral has three cleavage planes at right angles?
It forms cubic shapes. An example of this is galena.
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What happens when a mineral has three cleavage planes not at right angles?
It forms rhombic shapes. An example of this is calcite.
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How many cleavage planes does quartz have?
None! Some minerals don't have planes of weakness, they fracture instead. Fracture surfaces are not flat planes, e.g. the conchoidal fracture that occurs in quartz.
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How do we work out hardness?
We use a scratch test. Harder minerals scratch the softer minerals.
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How do we measure hardness?
We use Moh's scale of hardness.
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How does Moh's scale work?
It ranks ten standard minerals 1-10, 10 being the hardest (diamond) and 1 the softest (talk).
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What is lustre?
The way in which a mineral reflects light.
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What are the three ways we can describe lustre?
Metallic (shiny like metal), vitreous (glassy) and dull (not shiny).
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What is an example of a metallic mineral?
Galena
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What is an example of a vitreous mineral?
Quartz
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How do we know if a mineral contains carbonate?
It fizzes (gives off carbon dioxide) when you put it with dilute hydrochloric acid.
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How do we know if a mineral contains sulphide?
It smells like rotten eggs (gives off hydrogen sulphide) when you put it with dilute hydrochloric acid.
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What do we mean by form/habit?
The shape of the mineral, it is often controlled by the cleavage.
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