Labradorite is a member of a series of sodium and calcium silicate minerals known as plagioclase feldspars. Feldspars are major constituents of rocks and seldom are transparent or attractive enough to fashion into gemstones. Labradorite sometimes forms transparent crystals in volcanic rocks known as basalt. These crystals, called phenocrysts, are usually quite small and pale yellow in color. But in some localities, such as in northern Mexico, they can be up to several inches across and completely transparent. These crystals can be faceted into bright and attractive gemstones. Gem feldspars with the composition of labradorite are known in the gem trade as sunstone. The gemstones pictured, ranging in size from about 24 to 36 carats, are a unique variety that has been trade named Golden Sunstone.