Definition
Through Igneous and Metamorphic rocks
- In igneous and metamorphic rocks minerals may occur in the cracks, crevices, faults and joints.
- The smaller occurrences are called veins and the larger 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 and lead etc. are obtained from veins and lodes
Through the layers of Sedimentary rocks
In sedimentary rocks a number of minerals occur in beds or layers. They have been formed as a result of deposition, accumulation and concentration in horizontal strata
Decomposition of Surface Rocks
- When decomposition of surface rocks and the removal of soluble constituents takes place, it leaves a residual mass of weathered material containing mineral ores. Bauxite is formed by the decomposition of surface rocks.
- Alluvial deposits or Placer deposit : Some minerals are found in sands of valley floors and at the base of hills. These are known as placer deposits’. They are not corroded by water, example:- gold, silver, platinum and tin.
- Ocean Waters :-These contain many minerals. Common salt, magnesium and bromine are derived from ocean waters, whereas manganese nodules occur in ocean beds
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Flashcards
What are the modes of occurrence of minerals? ?
- Igneous / Metamorphic Rocks - tin, copper, zinc and lead etc
- Sedimentary Rocks
- Decomposition of Surface Rocks.