MODE OF OCCURENCE OF MINERALS :
Where are minerals found?
- Minerals are usually found in ores.
- Ore is used to describe an accumulation of any mineral mixed with other elements.
- Mineral content in one ore should be sufficient to make its extraction commercially viable.
Formations in which minerals generally occur in
- Igneous and Metamorphic rocks
- Sedimentary rocks
- Decomposition of surface rocks
- Alluvial deposits
- Ocean waters
IN IGNEOUS AND METAMORPHIC ROCKS :
- Minerals may occur in cracks, crevices, faults or joints.
- Smaller occurrences are called veins and larger ones are called lodes.
- In most cases, they are formed when minerals in liquid/ molten and gaseous forms are forced upward through cavities towards the earth’s surface. They cool and solidify as they rise.
- Major metallic minerals like tin, copper, zinc, lead, etc. are obtained from veins and lodes.
IN SEDIMENTARY ROCKS
- They have been formed as a result of deposition, accumulation and concentration in horizontal strata.
- Coal and some forms of iron ore have been concentrated as a result of long periods under great heat and pressure.
- Sedimentary minerals also include : Gypsum, potash salt, sodium salt.
- They are formed as a result of evaporation especially in arid regions.
DECOMPOSITION Of SURFACE ROCKS :
- Another mode of formation involves DECOMPOSITION OF SURFACE ROCKS or removal of soluble constituents , leaving a residual mass of weathered material containing ores.
- Bauxite is formed this way.
- a number of minerals occur in beds or layers.
ALLUVIAL DEPOSITS :
- Certain minerals occur as alluvial deposits in sands of valley floors and base of hills.
- These deposits are called ‘ placer deposits’ and contain minerals, which are not corroded (destroyed) by water.
- Gold, silver, tin and platinum are most important among such minerals.
OCEAN WATERS :
- Contain vast quantities of minerals, but most of these are too widely diffused to be of economic significance.
- Common salt, magnesium, bromine are largely derived from ocean waters.
- The ocean beds are rich in manganese nodules.
