Which geological environment is commonly associated with forming amethyst, aquamarine, chrysoberyl, citrine, moonstone, tourmaline, topaz and spessartine garnet?

• A. Alluvial deposits
• B. Pegmatites
• C. Metamorphic veins
• D. Kimberlite pipes

Answer: (B)

Pegmatites are coarse-grained, late-stage granitic rocks that crystallize from volatile-rich melts. This highly hydrated environment concentrates Be, Li, B, Mn, and other elements, allowing crystals to grow exceptionally large and forming mineral pockets rich in gemstones. That combination makes pegmatites the classic source for gemstones such as amethyst, aquamarine, chrysoberyl, citrine, moonstone, tourmaline, topaz, and spessartine garnet, all of which occur readily in these gem-rich pockets. While alluvial deposits can transport crystals and metamorphic veins or kimberlite pipes yield other mineral groups, pegmatites best account for this specific suite of minerals.