Q. Consider the following statements:

1. Sedimentary rocks
2. Decomposition of surface rocks
3. Igneous rocks
4. Metamorphic rocks

In which of the above mentioned forms minerals usually occur?
Answer: All of the above
Notes: In igneous and metamorphic rocks minerals may occur in the cracks, crevices, faults or joints. In sedimentary rocks a number of minerals occur in beds or layers. 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.