Minerals and their types

Mineral: a mineral may be defined as a natural substance, usually inorganic having a definite chemical composition and a definite molecular arrangement which is usually expressed in the geometric form.

 e.g. quartz (SiO2), orthoclase (KAlSi3O8), calcite (CaCO3), olivine [(Mg, Fe)2 SiO4] and gypsum (CaSO4.2H2O), halite NaCl

About 3000 minerals;> 500 are silicates; 50 minerals are widespread

Classification of minerals

Minerals can be classified on the basis of their mode of origin, composition and specific gravity are given below:

(A) On the basis of origin and mode of formation

1. Primary minerals

When a mineral arises from the cooling and solidification of a molten mass is called primary minerals.

e.g. (i) orthoclase feldspar - KAlSi3O8,

(ii) plagioclase feldspar- NaAlSi3O8,

(iii) anorthite feldspar - Ca(Al2Si2O8),

(iv) quartz - SiO2,

(v) hornblende - Ca2Al2Mg2Fe3. Si6O22(OH)2,

(vi) muscovite - KAl3Si3O10(OH)2 ,

(vii) biotite -KAl(Mg.Fe)3 Si3O10(OH)2

2. Secondary minerals

When it arises through the metamorphism or weathering of primary or other pre-existing minerals, it is called secondary minerals

e.g. (i) calcite - CaCO3

(ii) magnesite – MgCO3

(iii) dolomite - CaMg(CO3)2

(iv) siderite - FeCO3

(v) gypsum - CaSO4.2H2O

(vi) apatite - Ca5(F, Cl) (PO4)3

(vii) limonite - Fe2O3.3H2O

(viii) hematite - Fe2O3

(ix) gibbsite - Al2O3. 3H2O

(B) On the basis of chemical composition

According to their chemical composition, minerals are divided into eight groups.

1. Silicate: These are the salts of silicic acid (H4SiO4).

e.g. (i) muscovite - KAl3Si3O10(OH)2

(ii) biotite - KAl(Mg.Fe)3 Si3O10(OH)2

(iii) orthoclase feldspar - KAlSi3O8

(iv) zeolite - CaAlSi7O8.7H2O, SiO4

2. Native elements: The minerals of this group are made up of only one element.

(i) graphite – C, (ii) diamond – C, and (iii) sulphur – S.

3. Oxides e.g. (i) quartz - SiO2, (ii) hematite - Fe2O3, (iii) geothite - Fe2O3. H2O, 

(iv) Limonite - Fe2O3. 3H2O, (v)

magnetite - Fe3 O4, (vi) pyrolusite - MnO2, (vii) rutile - TiO2 and 

(viii) gibbsite - Al2O3.3H2O.

4. Sulphate e.g. (i) gypsum - CaSO4. 2H2O, (ii) barite - BaSO4

and (iii) gypsum anhydrite - CaSO4.

5. Carbonate e.g. (i) calcite - CaCO3, (ii) magnesite - MgCO3

and (iii) dolomite -CaMg(CO3)2

6. Sulphide e.g. (i) copper pyrite - CuS2 and (ii) iron pyrite - FeS2

7. Phosphate e.g. (i) apatite - Ca5 (F, Cl, OH, O)(PO4)3 Apatite is the source of P in soils.

8. Halides e.g. (i) flurorite (Flurospar) - CaF2 , (ii) rock salt (Halite)- NaCl and

 (iii) sylvite- KCl