Ключевые слова: abstract, america, amethyst, amethystgrotto, background, birthstone, brazil, calcite, crystal, deposit, detail, dig, druse, extraction, february, gem, gemology, gemstone, geode, geological, gramado, inclusion, jewel, lapidary, lode, luster, lustre, materials, mineral, mineralogy, mining, ore, polished, purple, quartz, rio grande, rock, semiprecious, shiny, south, stone, subsurface, texture, treasure, underground, valuable, vein, violet, vitreous,