Minerals in Earth Crust

 

1. Earth's resources are materials found in nature that are useful or necessaryto living things. Minerals are non-renewable Earth's resources.

 

2. The Earth's crust contains vast mineral resources. Materials used in buildings, furniture, cars and engines are all found within minerals from the Earth's crust.

 

3. Photograph 6.1 shows some rocks in the Earth's crust which contain minerals.

     

 

4. For centuries, human beings have dug rocks out of the Earth's crust for the useful minerals.

 

5. Minerals are elements or compounds which occur naturally in the Earth's crust.

 

6. Most minerals in rocks are natural compounds which are formed when elements combine chemically.

 

7. For instance, oxygen, carbon and metals such as copper combine chemically to form copper carbonate. Copper carbonate is an example of a mineral.

 

8. Other than carbonates, examples of natural compounds are oxides, sulphides and silicates.

 

9. However, there are minerals which are found as natural elements.

 

10. Examples of natural elements are gold, silver and diamonds (pure carbon).

 

Elements In Natural Compounds

1. Natural compounds are mostly compounds of oxygen, silicon, carbon or sulphur which combine chemically with one or more metals.

 

2. When oxygen combines with metals chemically, oxides are formed.

                        Metal + oxygen → Metal oxide

 

3. Examples of oxides are iron oxide, copper oxide and magnesium oxide.

 

4. Carbonates are compounds that contain oxygen, carbon and metals.

                  Metal + oxygen + carbon → Metal carbonate 

 

5. Examples of carbonates are sodium carbonate, lead carbonate and zinc carbonate.

 

6. When sulphur combines with metals, sulphides are formed.

                       Metal + sulphur → Metal sulphide

 

7. Examples of sulphide are copper sulphide and silver sulphide.

 

8. Silicates are formed when metals combine with oxygen and silicon chemically.

                  Metal + silicon + oxygen → metal silicate

 

9. Examples of silicates are calcium silicate and magnesium silicate.
 

Natural compound

Examples

Element existing in it

Oxides

- Iron oxide

- Aluminium oxide

- Iron, oxygen

- Aluminium, oxygen

Carbonates

- Copper carbonate

- Sodium
  carbonate

- Copper, carbon, oxygen

- Sodium, carbon, oxygen

Sulphides

- Lead sulphide

- Zinc sulphide

- Lead, sulphur

- Zinc, sulphur

Silicates

- Magnesium
  silicate

- Calcium silicate

- Magnesium, silicon,
  oxygen

- Calcium, silicon, oxygen

 

         Properties Of Minerals:-

Hardness of minerals

(a) Hardness of minerals is the ability of minerals to resist being scratched.

 

(b) We can determine a mineral’s hardness by rubbing the mineral against objects
      such as nails, coins or a fingernail.

 

(c) Soft minerals are scratched easily.

 

(d) The softest minerals can be scratched with the fingernail.

 

(e) Diamond is the hardest mineral.

Reactivity and solubility

(a) Minerals that exist in the Earth’s crust as natural elements are non-reactive
     elements.

 

(b) These elements tend to remain as elements without combining with any other
      substances.

 

(c) Most of the minerals that exist in the Earth’s crust as natural compounds are
     hard and do not dissolve in water.

Effects of heat on minerals

(a) Most oxides are stable compounds and do not decompose when they are heated.
     However, oxides formed by non-reactive metals such as gold and silver will
     decompose to give pure metals and oxygen when heated.

 

(b) Most carbonate compounds are not stable and will decompose into oxides and
     carbon dioxide when heated.

Example:
\(Copper\quad carbonate\quad \underrightarrow { heat } \quad Copper\quad oxide\quad +\quad carbon\quad dioxide\)

However, sodium carbonate and potassium carbonate are stable and are not decomposed by heat.

 

(c) Most sulphide compounds are not stable and will be decomposed by heat into
     metal oxides and sulphur dioxide.

Example:
\(Magnesium\quad sulphide\quad +\quad oxygen\quad oxide\quad >\quad Magnesium\quad +\quad sulphur\quad dioxide\)