Mode of Occurrence (Minerals) - Concepts - Chapter 5 Class 10 Geography - Minerals and Energy Resources - Geography

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

1. Igneous and Metamorphic rocks
2. Sedimentary rocks
3. Decomposition of surface rocks
4. Alluvial deposits
5. 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.