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Minerals

 

The terrestial crust is formed by different materials. The most importan ones are minerals and rocks.

 

  • Minerals: They are substances that have to:

 

- Be solid at room temperature.

- Be inorganic: they cannot be formed by H+C

- Have a defined chemical composition: they are formed by one or more elements in a certain proportion that we can express with a chemical formula.

- Have a natural origin: they are not made up by humans.

 

  • Rocks: They are solid substances formed by the combination of minerals.

 

 

COMPOSITION OF MINERALS

 

The main chemical elements that form the composition of minerals are: oxygen (O), silicon (Si), aluminium (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K) and magnesium (Mg).

 

Other elements exist in very small proportion: carbon, gold, copper, uranium, etc.

 

Minerals can be classified by their chemical composition in two main groups:

 

  • Silicates: they are formed by the most frequent elements: oxygen and silicon. They are the most abundant minerals on the Earth. For example: quartz, feldspar, mica, olivine, etc.

 

  • Non-silicates: they are formed by other compounds and do not contain silicon. It can be distinguish several groups:

 

- Native elements: they are made up of a single element. For example, gold.

- Oxides: they are made up of oxygen and other element. For example, oligiste.

- Sulphides: they are made up of sulphur and a metal. For example, galena.

- Carbonates: they are made up of carbon, oxygen and a metal. For example, calcita.

- Halides: they are made up of a metal and chloride or fluoride. For example, halite.

ACTIVITIES

 

Search for new vocabulary and build up a particular section of related vocabulary.

 

1. Look at the chart and indicate why these substances cannot be considered minerals.

 

 

 

 

 

 

 

 

 

2. Which are the main differences between minerals and rocks?

 

 

3. What is the different between silicates and non-silicates?

 

4. Indicate the composition of:

 

a. Oxide                           b. Sulphide                            c. Carbonate                         d. Halide

 

 

5. Diamonds are %100 carbon. Which group of mineral do they belong to? Why? What are they made up of?

PROPERTIES OF MINERALS

 

They are physical characteristics that can be observed and determined in a simple way. The chemical composition and the disposition of the atoms influence many physical properties:

 

  • Density: it is the relationship that exists between the mass of the mineral and its volume.

 

  • Hardness: it is the resistence that the mineral has to being scratched. To definde the hardness of a mineral we use the Moss scale of hardness.

 

- If it can be scratched with your fingernail, it is soft (low hardness).

- If it does not scratch glass, it is hard (half hardness).

- If it scratches glass, it is very hard (high hardness).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  • Colour: it depends on the light that is absorbed or reflected by the mineral. some mineral have always the same colour, but others can have different colours because small differences in their chemical composition, such as quartz.

 

  • Streak: it is the colour of the mineral in powder form. This is constant in each one.

 

  • Shine: it is the aspect that the surface offers when reflecting light. It can have:

 

- metallic shine (as metals)

- adamantine (as diamond)

- pearly (as mother-of-pearl)

- silky (as silk)

- fatty (as oil)

- vitreous (as glass)

 

  • Exfoliation (or cleavage): it is the ability of a mineral to break easily in parallel sheets.

 

  • Diaphaneity: it is the grade of trasnparency of the mineral. It can be:

 

- opaque (if it does not allow light to pass)

- translucent (if it allows light to pass, but not images)

- transparent (if it allows light and images to pass)

 

 

ACTIVITIES

 

Search for new vocabulary and build up a particular section of related vocabulary.

 

1. Identify the property that is talking about in each sentence and complete it.

 

a. It is the resistence to be scratched. To measure it we use the......................................

b.The minerals can................................... If they do not have this property we say it is.............................

c. This property refers to the ability of a mineral to break along............................................

d. This property ...................... constant in each mineral and it refers to the colour of the mineral in powder.

e. Minerals can be transparent, translucent or.............................

 

2. Read the following description of the galena and identify the properties it is talking about:

 

"Galena is formed from lead sulfide (1). It is soft and easily breaks along the planes of a cube (2). It does not let light pass trough it (3) and it is deep shiny metal colour (4) and leaves a dark grey powder (5)."

 

3. Look at the Mohs scale and answer these questions:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

a. What minerals can be scratched with a fingernail?

b. What minerals can scratch glass?

c. Wich of the minerals is the hardest one? Can it scratch the rest of them?

d. What minerals are softer than Orthoclase? And harder?

 

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