51. JARGOON is a gem usually of smoky yellow or brownish colour, and sometimes limpid: if placed upon any object, it exhibits of it a very distinct double image.
The primitive form of its crystal is an octohedron ([Pl. II, Fig. 5]), but it is frequently crystallized in right-angled prisms, terminated by four-sided pyramids.
In hardness this stone does not much exceed that of the emerald. The greyish white and yellowish white varieties of jargoon are valuable chiefly on account of their resemblance to the diamond. The darker-coloured varieties can be deprived of their colour by heat; and, in this state, though in lustre they are infinitely inferior to them, they are sometimes substituted for diamonds. Jargoons are now seldom used except for the jewelling of watches and time-pieces. About a century ago, they were much used in mourning ornaments, for which the dark tone of their colour, and their almost adamantine lustre, were supposed to be peculiarly appropriate.
The jargoon is principally brought from the island of Ceylon; but it is occasionally found in France, and Spain, and in granite rocks near Cuffel, in Dumfrieshire, Scotland.
52. The Hyacinth, or Jacinth, is a dark orange-red variety of jargoon. It is also chiefly imported from Ceylon, where it is generally found in the sand of rivers, in irregularly round pieces, but seldom of large size without flaws.
This stone is indebted for its name to a supposed resemblance in colour to that flower, which, according to the Pagan mythology, Apollo raised from the blood of his favourite youth, Hyacinthus.
When bright, and free from flaws, the hyacinth is a superb ring stone; but it is not of usual occurrence in modern jewellery.
RUBY FAMILY.
53. The ORIENTAL SAPPHIRE is a gem of blue colour, the shades of which vary from a full and deep tint to a nearly colourless appearance, and sometimes it is party-coloured.
It is found crystallized in six-sided pyramids much lengthened and joined base to base ([Pl. II, Fig. 13]); and also in rounded or pebble-shaped fragments. It has a foliated texture, is extremely hard, and about four times as heavy as water.