No definite idea can be given in relation to the price of the opal, so much depends upon the degree of its brilliancy and play of colors. The gem is not sold by weight, but its value is estimated by its size and the perfection of its charms. An opal half an inch in diameter exhibiting fair colors may be worth $5, and another of the same size, of greater perfection, may bring $5,000, or more. The palmy days of the opal were during the period of Roman luxury, as the beauties of the diamond were not then fully revealed, and the opal flashed forth its marvellous beams of color both by daylight and artificial light. The gem then commanded enormous prices. According to the tables of Dureau de la Malle, the opal of Nonius was valued at twenty million sesterces, or about eight hundred thousand dollars. Enormous as this sum of money appears, Catherine of Russia would have given as much for the gem, if its beauty had been in keeping with its reputation. The commerce of the opal affords a curious example of credulity and superstition, which is in singular contrast with the progressive ideas of our advanced civilization. In times past the changes that sometimes occur in the opal from physical causes have impressed the minds of some excessively superstitious people as due to supernatural causes. And from these trivial fancies the most beautiful and _recherché_ of all that Nature has offered to us in the mineral kingdom has been placed under ban. This superstitious dread may be of ancient origin, and whence its source we know not. But it is a matter of history that the opal was the favorite gem among the Romans in their best periods of intelligence and refinement. So far from being feared at that time, it was eagerly sought for, as it was supposed to possess the power of warning against disaster, and exhibiting the rosy herald of joy. Hence it has been thought that a feeling of superstition as well as of avarice influenced Nonius when his paragon was demanded of him.