Joaquinite | Geology Page. Joaquinite, which was discovered in 1909, is a pretty rare mineral. It is most renown for its association with other exotic minerals such as the sapphire blue benitoite, the red-black neptunite and the snow white natrolite. If it were not for these minerals which are found in San Benito County, California; joaquinite might not be so well known. It forms typically small, sparkling, brown to yellow, well formed crystals usually scattered on massive green serpentine.