Multicolored Tourmaline stone & 14K gold chain convertible necklace, American, 1950s. Antique Reflections Gallery. Appropriately for the month with the best changing fall colors, October’s two birthstones, tourmaline and opal, are best known for their varied hues. According to EarthSky, tourmaline is a stone that “exhibits the broadest spectrum of gemstone colors. Gem-quality forms of […]