HYACINTH, in natural history, a genus of pellucid gems, whose colour is red with an admixture of yellow.
The hyacinth, though less striking to the eye than any other red gem, is not without its beauty in the finest specimens. It is found of various sizes, from that of a pin's head to the third of an inch in diameter. They are harder than quartz-crystals; transparent, and formed into prisms pointed at both ends. These points are always regular with regard to the number of facets; being four on each facet, but the latter seldom: the sides of the main body are also very uncertain, in regard both to their number and shape; being found of four, five, six, seven, and sometimes of eight sides; sometimes being so compressed as almost to resemble the face of a spherical faceted garnet. Sometimes they are of a dodecaedral form like the garnet, but with more obtuse angles. The specific gravity of the hyacinth, according to Dutans, is 2.631; but Rome de L'Isle says that Brisson found it to be 3.687; and the European hyacinths to be 3.760.
The hyacinth, as well as all other gems, is divided into oriental and occidental; the former being very hard and brilliant, so that they are frequently ranked among the topazes; but when soft, they are supposed to belong to the garnet kind, as mentioned under that article. The hyacinths, however, may generally be distinguished from the garnets by losing their colour in the fire, becoming white, and not melting. There is a kind of a yellow-brown hyacinth, resembling the colour of honey, which is distinguished from the rest by the remarkable property of not being electrical, and being likewise inferior in hardness.
Our jewellers allow all those gems to be hyacinths or jacints that are of a due hardness with the mixed colour above mentioned; and as they are of very different beauty and value in their several degrees and mixture of colours, they divide them into four kinds; three of which they call hyacinths, but the fourth, very improperly, a ruby. 1. When the stone is in its most perfect state, and of a pure and bright flame-colour, neither the red nor the yellow prevailing, in this state they call it hyacintha la belle. 2. When it has an over-proportion of the red, and that of a dusky colour than the fine high red in the former, and the yellow that appears in a faint degree in it is not a fine, bright, and clear, but a dusky brownish yellow, then they call it the saffron hyacinth. 3. Such stones as are of a dead whitish yellow, with a very small proportion of red in them, they call amber-hyacinths. And, 4. When the stone is of a fine deep red, blended with a dusky and very deep yellow, they call it a rubacelle.
Hyacinthus But though the over proportion of a strong red in Hyacinthis, this gem has made people refer it to the class of rubies, its evident mixture of yellow shows that it truly belongs to the hyacinth.
The hyacinth la belle is found both in the East and West Indies. The oriental is the harder, but the American is often equal to it in colour. The rubacelle is found only in the East Indies, and is generally brought over among the rubies; but it is of little value: the other varieties are found in Silesia and Bohemia.