Occurrence of Metals

         Element which have low chemical reactivity generally occur native or free or metallic state. For example Au, Pt noble gas etc. Element which are chemically reactive, usually occur in the combined state. For example chalcogens, halogens, etc. The natural materials in which the metals occur in the earth are called minerals. Mineral out of which the metal is conveniently and economically extracted is termed as ore. All the ores are considered as minerals but all the minerals cannot be considered as ores. Ores can be divided into four groups,

         (1) Metallic core (siderophile) of the earth crust contains (Mn, Fe, Co, Ni, Cu, Ru, Rb, Pd, Ag, Re, Os, Ir, Pt, Au). The whole composition of metals in earth crust can be given as,

         Al (8.3%); Ca(3.6%); Na (2.8%); K (2.6%); Mg (2.1%); Ti (0.4%); Mn (0.1%); Fe (5.1%) other metals (0.1%).

         (i) Native ores: These ores contain metals in free state, for example gold, mercury, silver, platinum, copper, etc. These can be found commonly associated with rock or alluvial materials such as clay, sand, etc. sometimes the lumps of pure metals are also found. These are called as nuggets. Iron is found in free state as meteroites which also posses 20 to 30% nickel.

         (ii) Sulphurised and arsenical ores : These ores consist of sulphides and arsenides in simple and complex forms of metals. The significant ores of this group are

         (iii) Oxidised ores : In these ores, metals are present as their oxides or oxysalts such as carbonates, nitrates, sulphates, phosphates, silicates, etc.

         Main ores of this group are listed below,

         Oxides

Carbonates

Nitrates

Sulphates

Phosphates and Silicates

        (iv) Halide ores : Metallic halides are very few in nautre. The chlorides are most common. Examples of it are as follows

         Common salt NaCl;     Horn silver AgCl

         Carnallite KCl.MgCl₂.6H₂O

         The important fluoride ores are

         Fluorspar CaF₂;      Cryolite Na₃AlF₆

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