278                                Pearls,
	in appearance very like an opal ; the summit dis­playing a radiating lustre. Probably this Pearl was obtained from the great clam shell—a shell which occasionally produces Pearls, but of no value, being lustreless, and not to be compared even with a common fresh-water Pearl.
	Pearls of various other Colours. Respecting Pearls of other colours than black and pink, very little need be said. The grcenüh-black is probably of all tints most coveted ; it occurs, however, but rarely, and when a Pearl of this parti­cular hue, possesses the right orient, it exceeds in value all other coloured Pearls. A bluish-black Pearl, if of fine orient, is almost as valuable as a true black one. The Pearls from the Ρ lacuna placenta are often of a dull leaden colour, while those occasionally found in the outer coat of the Pinna squamosa are commonly of a brown tint, Brown Pearls are of very little value ; neither are those of plutn-colour much sought after. Red Pearls are worth only about one shilling per grain. Yellow Pearls again do not generally realize more than a few shillings per grain, and those of gamboge tint are practically of no value in this country. When, however, a Pearl is of a very fine bright golden colour, it may be worth from twenty to forty shillings per grain.