Opals[3049] are at once very similar to, and very different from, beryls, and only yield to the smaragdus in value. India, too, is the sole[3050] parent of these precious stones, thus completing her glory as being the great producer of the most costly gems. Of all precious stones, it is opal that presents the greatest difficulties of description, it displaying at once the piercing fire of carbunculus,[3051] the purple brilliancy of amethystos, and the sea-green of smaragdus, the whole blended together and refulgent with a brightness that is quite incredible. Some authors have compared the effect of its refulgence to that of the colour known as Armenian[3052] pigment, while others speak of it as resembling the flame of burning sulphur, or of flame fed with oil. In size, the opal is about as large as a hazel-nut,[3053] and, with reference to it, there is a remarkable historical anecdote related. For there is still in existence a stone of this class, on account of which Antonius proscribed the senator Nonius, son of the Nonius Struma, whom the poet Catullus[3054] was so displeased at seeing in the curule chair, and grandfather of the Servilius Nonianus, who in our own times was consul.[3055] On being thus proscribed, Nonius took to flight, carrying with him, out of all his wealth, nothing but this ring, the value of which, it is well known, was estimated at two millions of sesterces. How marvellous must have been the cruelty, how marvellous the luxurious passion of Antonius, thus to proscribe a man for the possession of a jewel! and no less marvellous must have been the obstinacy of Nonius, who could thus dote upon what had been the cause of his proscription; for we see the very brutes even tear off the portion of their body for the sake of which they know their existence to be imperilled,[3056] and so redeem themselves by parting with it. CHAP. 22.—DEFECTS IN OPALS: THE MODES OF TESTING THEM. Defects in opal are, a colour inclining to that of the flower called heliotropium,[3057] or to that of crystal or of hailstones; salt-like grains intervening; roughness on the surface; or sharp points, presenting themselves to the eye. There is no stone that is imitated by fraudulent dealers with more exactness than this, in glass, the only mode of detecting the imposition being by the light of the sun. For when a false[3058] opal is held between the finger and thumb, and exposed to the rays of that luminary, it presents but one and the same transparent colour throughout, limited to the body of the stone: whereas the genuine opal offers various refulgent tints in succession, and reflects now one hue and now another, as it sheds its luminous brilliancy upon the fingers.