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 in microscopic layers of varying chemistry, and these layers produce an optical effect known as 'Schiller', seen as a colored reflective 'sheen' coming from within the material. The colors may vary depending on locality, orientation and chemical composition. Bright blue-sheen labradorite is best known from the Malagasay Republic (Madagascar), and is often fashioned into cabochon gems and decorative objects.