‘Minerals occur in various forms.’’ Support this statement with examples.
Answer to be written in the exam
1. 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.
- Major metallic minerals like tin, copper, zinc, lead, etc. are obtained from veins and lodes.
2. 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.
3. 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.
4. 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.
5. 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.
(all 5 subheadings to be explained ; 1x5)