Three main types of formations in which mineral occurs are
(i) Veins and lodes In igneous and metamorphic rocks minerals may occur in the cracks, crevices, faults or joints. Smaller occurrences are called veins and larger ones are called lodes.
(ii) Beds or Layers In sedimentary rocks, minerals occur in bed or layers. They are formed as a result of deposition, accumulation and concentration in horizontal strata, (layers)
(iii) Placer Deposits Certain minerals occur as alluvial deposits in sands of valley floors and the base of hills as placer deposits.