Minerals occur in various forms. Support this statement with examples.

Minerals generally occur in these forms:

1. In igneous and metamorphic rocks, minerals may occur in the cracks, crevices, faults, or joints. The smaller occurrences are called veins, and the larger is 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.
   
   
2. 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.
   Coal and some forms of iron ore have been concentrated as a result of long periods under great heat and pressure. Another group of sedimentary minerals includes gypsum, potash salt, and sodium salt. These are formed as a result of evaporation, especially in arid regions.
   
   
3. Another mode of formation involves the decomposition of surface rocks, and the removal of soluble constituents, leaving a residual mass of weathered material containing ores. Bauxite is formed this way.
   
   
4. Certain minerals may occur as alluvial deposits in sands of valley floors and the base of hills. These deposits are called ‘placer deposits’ and generally contain minerals, which are not corroded by water. Gold, silver, tin, and platinum are the most important among such minerals.
   
   
5. The ocean waters contain vast quantities of minerals, but most of these are too widely diffused to be of economic significance. However, common salt, magnesium, and bromine are largely derived from ocean waters.
   The ocean beds are rich in manganese nodules.