Unit 4: Minerals and rocks                                                       1   2   3   4

2.2. 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 resistance that it has to being scratched.

     To define it 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).

- Color: It depends on the light that is absorbed or reflected by

  the mineral. Some mineral have always the same color,

  but others can be different colors 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 (or lustre): 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)

    - fatty (as oil)

    - silky (as silk)

    - vitreous (as glass), etc.

- Exfoliation (or cleavage): It is the ability of a mineral to break easily

   in parallel sheets.

- Diaphaneity: It is the grade of transparency of the mineral.

  It can be:

     - opaque (if it doesn't allow light to pass)

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

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

2.7. Identify the property that is talking about in each sentence

       and cross out the italics incorrect option:

a.  It is the resistance to be scratched. To measure it

     we use the Mohs scale / Grade of transparence

b.  The minerals can be metallic / vitreous or non-metallic. 

     If they don´t have this property, it is dull / transparent.

c. This property refers to the ability of a mineral

     to break along fragments / planes of weakness.

d. This property is /is not constant in each mineral

    and it refers to the colour of the mineral in powder.

e.  Minerals can be transparent, translucent or dull / opaque.

2.8. Read the following description of the galena and identify

       the properties it is talking about:

    “Galena is formed from lead sulfide (PbS) (1).

    It is soft and easily breaks along the planes of a cube (2).

    It doesn’t let light pass trough it (3)

    and it is a deep shiny metal colour (4)

    and leaves a dark grey powder (5).”

2.9. Look at the Mohs scale and answer the questions:

    a. What minerals can be scratched with a fingernail?

    b. What minerals can scratch glass?

    c. Which of the minerals is the hardest one?

        Can it scratch the rest of them?

    d. What minerals are softer than Orthoclase?

        What minerals are harder?

    e. What number has Orthoclase in the Mohs scale?

        And the rest of minerals?

2.10. Listen and indicate what mineral property is described: