# A Treatise on Diamonds, and Precious Stones/Chapter 2/Section 7

SECT. VII.
Amethyst, Yellow Crystal, Rock Crystal, and Cat's Eye, Sard & Onyx, Opal, and Chrysoprase.
These substances belong to the same class, and differ chiefly in color and translucency. The color of the Amethyst, when perfect, resembles that of the violet or purple grape; but it not unfrequently happens, that the tinge is confined to one part of the stone only, while the other is left almost colorless. When it possesses a richness, clearness, and uniformity of hue, it is considered a gem of exquisite beauty; and as it occurs of considerable size, it is suited to all ornamental purposes.
​In specific gravity and hardness, it bears no comparison with the oriental amethyst; it is also inferior in beauty and lustre; though I have often seen the common amethyst offered for sale as Oriental.
Brazil, Siberia, and Ceylon, produce very fine amethysts: they are found in rolled pieces in the alluvial soil, and finely crystallized in fissures of the rock, From the first of these localities, they have lately been imported in such quantities, as considerably to diminish their value: but, as they are the only colored stones, except garnets, that are worn with mourning, they still retain, when perfect, a distinguished rank among the precious gems.
The present price of inferior light colored stones, in the rough state, is about twenty shillings per pound, whilst those of good quality sell at ten or twelve shillings per ounce. Ame​thysts calculated for brooches or seals, may be purchased at from fifteen shillings to two or three guineas each, for which, ten years ago, treble that sum would have been given.
The amethyst shews to the greatest advantage when cutin steps, with double work upon the bizel; and the table and facets proportioned according to the intensity of the color. A perfect stone, when turned out of hand by a good workman, is a beautiful gem; it contrasts well with fine gold setting, and when surrounded with brilliants has a rich and splendid effect, but alone it loses much of its beauty by candle-light,
YELLOW CRYSTAL—CAIRNGORHM
Is of a beautiful yellow color, and of different shades, from deep to light yellow; also smoky and brown. It is used in various ornaments, ​as necklaces, &c. but more generally in seals and brooches. Stones sufficiently large for this purpose, may be purchased at from five to ten or fifteen shillings each, and inferior for considerably less.
This substance has also been lately imported in large quantities from Brazil, which has so overstocked the market, that it is now selling at from fifteen shillings to two guineas per pound; whereas a few years ago it sold for three guineas per ounce: it is a beautiful stone, and will most likely become more valuable.—It is often set on foil, and sold for topaz, which it much resembles, but is less brilliant.
ROCK CRYSTAL
Is a transparent substance proverbially clear. It occurs massive and crystallized, filling veins and crevices of rocks; also in rolled pieces in ​the alluvium, and may be said to be generally distributed in all parts of the world. Small pebbles of crystal are often collected in the vicinity of London, as Bagshot, &c.. which, on account of their cutting glass, and shining when polished, are called diamonds.—We have also Irish and Cornish diamonds belonging to the same class.
Crystal receives a good polish, and is worked into an immense variety of forms; it is much used in jewellery, and commonly set on foil. Larger pieces are cut for the glasses of spectacles, hence called Pebble Spectacles. It is a substance in very general demand, and sells at from two shillings to ten shillings per pound.
THE CAT'S EYE
Is considered to be a variety of crystal, enveloping amianthus.
​It is a common substance in Ceylon, from whence great quantities are annually received. It presents a peculiar luminous appearance when held in a strong light, resembling the eye of the animal from which it is named. Its color is generally light grey, yellowish, or reddish brown: a variety, of rare occurrence, is dark green, which exhibits more strongly and in greater perfection the same characters, and is much more valuable and highly prized.
Fine specimens of this stone are held in high veneration by the Cinglese. They are generally used for ring stones, and cut hemispherically,
SARD OR SARDOINE AND ONYX
Are terms not very distinctly understood; they are frequently confounded by writers on mineralogy, and still more so by lapidaries.
​The sard or sardoine is considered to be a beautiful variety of chalcedony, and,when perfect, of one uniform tone of color, which is yellowish brown, or reddish brown, of lighter or darker tints, sometimes approaching black; it is more or less translucent when held between the eye and a strong light. When it exhibits angular lines of lighter colors, it is called Oriental Agate. It is generally found in the alluvial soil, and has often been met with in searching for gold and diamonds. It also oceurs stalactitic and forming geodes.
The ancients selected this substance, and the following variety, to engrave upon, no doubt from its possessing two peculiar and necessary qualities, namely hardness and tenacity, by which it is capable of receiving the ​finest touch or stroke of the tool without chipping, and shewing the art of the engraver to the highest perfection.
Any stone exhibiting layers of two or more colors, strongly contrasted, is called Onyx: as banded jasper, chalcedony, &c. but more particularly the latter, when it is marked with white, and stratified with opaque and translucent lines. But the oriental onyx is considered a substance consisting of two or more layers or bands of distinct and different colors. A sard or sardoine, having a layer of white upon it, would be called an Onyx; and according to the number of layers, it would be distinguished as an onyx with three or more ​bands: some of the antique engravings are upon onyxes of four bands.
THE PRECIOUS OPAL.
The color of the opal is white or pearl grey, and when held between the eye and the light is pale red, or wine yellow, with a milky translucency. By reflected light it exhibits, as its position is varied, elegant, and most beautiful iridescent colors, particularly emerald green, golden yellow, flame and fire red, violet purple, and celestial blue, so beautifully blended, and so fascinating, as to captivate the admirer. When the color is arranged in small spangles, it takes the name of the Harlequin Opal.—Sometimes it exhibits only one of the above colors, and of these the most esteemed are the vivid emerald green, and the orange yellow. When the stone possesses the latter of these colors, it is called the Golden Opal.
​The precious opal is not quite so hard as rock crystal; it is frequently full of flaws, which greatly contributes to its beauty, as the vivid iridescent colors which it displays are occasioned by the reflection and refraction of light, which is decomposed at these fissures, It is never cut in facets, but always hemispherical. It is generally small, rarely so large as an almond or hazel nut, though I have seen some specimens the size of a small walnut, for which several hundred pounds were demanded. At present,a pretty opal may be bought at from one to three, or five guineas, sufficiently large for a pin, or ring stone. It requires great care and judgment in the cutting, as it is fragile, and easily spoiled,
The opal in all ages has been highly esteemed; the history of the Roman senator, who preferred death rather than give up his opal ring to the emperor Nero, is familiar to ​every one. Among the Eastern nations the opal ranks higher than in Europe.
A spurious substance is sometimes sold for black and green opal, and is often set in jewellery; it ocurs of the size of a small almond, but more commonly not larger than a lentil or pea. This precious gem is nothing more than the cartilage of the hinge of a large shell. Glass, and even scoria, having an iridescent appearance, have also often been sold for opal.
THE CHRYSOPRASE
Is of a cloudy pale green color, and has an agreeable appearance: it is translucent, and shews to advantage by. candle-light, more particularly if surrounded by small brilliants.
a Chrysophase of fine quality, and sufficiently large for a brooch or a seal, is worth from two to four or five. guineas. It does not admit of being cut with facets, except round the bizel, which should be low, and the under siderounded. Inferior stones are common, and very low priced.
Carnelians are often extremely beautiful, and deservedly much esteemed, as are varieties of fine mocha stones, agates, and jaspers, whose peculiar characters are strikingly attractive. They are, generally speaking, the most common ornaments set in jewellery, but are not ranked in the class of precious stones.
* ↑ The Sard or Sardoine owes its derivation to Sardis, a city of Minor Asia, where a peculiarly fine variety of chalcedony and agate is occasionally found.
* ↑ This stone derives its name from the resemblance which some varieties bear to the marks on the finger nail, and has been extended to all stones haying a banded appearance.
* ↑ See Appendix.