In hindy mythology there are three kinds of gems they are gems from swargloka , gems from patalaloka , gems from marthyaloka .
1. These gems are available out of some ascetic’s austere penance acquired from the divine power .
2 . We hear about many divine gems in mahabharat and mythological books such as swamnatak , kousthubh mani etc ( cf matsya puranata chapter 45 page 159 ) .
3. It is believed tht during the influence of the constellation called swati governed by the rahu if the rain drops fall upon the oyster shells they turn into pearls after sometime . The showering rain drops get dry often in air and become another kind of pearl called chintamani pearl ( cf ratnaparikshadi sapta grantha sangraha page number 20 )
4. Varahmihira believed that there are some divine gems or pearls which drop from sky like the hails but dames in the heaven take all of them away before they actually land on earth ( cf vrihatsamhita chapter 81 / sloka 24 page 493 .
5 . Swargloka gems are called mani they are chintamani white in color worn by lord brahma , koustuba mani like lotus red in color , worn by lord krishna & lord vishnu , rudramani yellow golden in colour worn by lord shiva , shymanthakmani blue in color worn by lord indra .