Opal

In the Middle Ages, opal was considered a stone that could provide great luck because it was believed to possess all the virtues of each gemstone whose color was represented in the color spectrum of the opal. However, modern superstition attributes bad luck to the stone, though some believe this is avoided if opal is the owner's birthstone (that is, the owner was born in October) or if the stone is a gift. Even under the last czar at the beginning of the 20th century, it was believed that when a Russian of any sex, of any rank, saw an opal, amongst other goods offered for sale, he or she would not buy anything more, since, in the judgement of subjects of the czar, the opal embodied the evil eye. It's possible that the stone's extreme fragility (when compared to other gemstones) has contributed to this bad reputation.

The opal is a very soft gemstone.