Name the chief forms of the occurrence of the following in the earth's crust :
(a) Aluminium
(b) Calcium
(c) Sodium
(d) Lead

Explanation

(a) Aluminium
(i) Corundum `Al_(2)O_(3)`
(ii) Diaspore `Al_(2)O_(3). H_(2) O`
(iii) Bauxite `Al_(2) O_(3).2H_(2) O`
Halides : Cryolite `Na_(3)AlF_(6)`
Silicates :
(i) Feldspar `KAlS_(3)O_(8)`
(ii) Mica `KAlSi_(3)O_(10)(OH)_(2)`
(b) Calcium :
Carbonate : Lime stone `(CaCO_(3))` , marble, chalk, calcite, and dolomite `(MgCO_(3).CaCO_(3))`
Sulphates : Gypsum, `CaSO_(4).2H_(2)O` and anhydride, `CaSO_(4)`.
Fluoride : Fluorspar, `CaF_(2)`
Fluorapatite, `3Ca_(3)(PO_(4))_(2) CaF_(2)`
Phosphate : Phosphorite, `Ca_(3)(PO_(4))_(2)`.
( c) Sodium :
Sodium chloride, `NaCl`
Sodium nitrate or chile saltpetre : `NaNO_(3)`
Sodium carbonate : `Na_(2)CO_(3)`
Borax : `Na_(2)B_(4)O_(7). 10H_(2)O`.
(d) Lead :
Anglesite : `PbSO_(4)` Cerussite : `PbCO_(3)`
Lanarkite : `PbO.PbSO_(4)`.