Opal is the name of a gemstone, the English form of Greek opallios which is derived from Sanskrit upala meaning “gem, stone”. Opals are the birthstone of October. The Romans considered them as a symbol of hope, purity, and good fortune and were thought to have healing powers. According to the ancient Greeks, they believed opals were formed from the tears of the god Zeus and believed that it gave one the gift of prophecy and foresight. In ancient India, the opal was thought to represent the Goddess of Rainbow who turned herself into an opal to avoid the advances of the other gods. Arab lore held that the opal had falen from the sky with lightning trapped inside it, and that it could make the wearer invisible. The Aborigines of Australia considered the opal sacred; according to their mythology, the creator spirit came down to earth on a rainbow and when it touched the ground, it turned the rocks to opals.
However, despite their positive associations, opals also took on an unfortunate property and were considered to be bad luck.