Opal is the October birthstone. These precious gems form from centuries upon centuries of seasonal rains that leach microscopic silica particles from sandstone, carrying them deep into underground fissures and cavities. As the deposited materials dry, the microscopic silica spheres become compressed into a closely-packed lattice. As light travels through this microstructure, it creates a dazzling kaleidoscope of flashing rainbow colors, called "play-of-color". Australia has long been the epicenter of the opal industry, fueled by early opal rushes in the Victorian era and later discoveries in the 20th century. The Ethiopian variety of opal was somewhat newly discovered in the 1990's in the steep volcanic cliffs that border the Great Rift Valley in Ethiopia. With its abundance of spectacular, "play-of-color" opals, Ethiopia is known as the modern opal capital of the world -- taking the throne from Australia.