ADULARIA. ORTHOCLASE.
This stone is so called from Adula, the Latin name of Mount St. Gothard, as the best kind is obtained there, and particularly from that part called the ” Monte della Stella.” Adularia belongs to the felspars, of which it is the purest kind. Its crystals have one of the facets deeply indented in the direction of the greater diagonal. Their primitive nodus is an oblique prism with rhomboidal sides, whose base is an oblique angled parallelogram ; the secondary forms present an oblique prism with four facets, a large rectangular prism, a tablet with six facets, and a rectangular prism with six facets.
Masses of rough adularia are found in which there frequently exist double crystals, and yet in this state of perfect union they have different degrees of hardness. Some also are opaque, others translucent or clear. This union of massed crystals causes the iridescence which often distinguishes those found in Italy, France, Germany, Norway, America, and the Isle of Ceylon. That which comes from the Monte Stella is transparent, and has whitish reflections tinted with green and blue ; some pieces shine with pearly light.
Others are of an iridescent green colour which resembles the eye of a fish ; which often, in very thin lamina, becomes by reflection a pale rose colour. This gem is remarkable for its brightness, which may compare equally with that of pearl and glass. It is very easily worked, having three cleavages, and has double refraction. Its cleavage is perfectly concave. Being altogether destitute of electricity, it does not act on the magnetic needle. When exposed to the action of the blow-pipe it melts into a transparent white glass. Its specific weight is 2-5. The heat, 0.1861.
Although adularia scratches rock crystal, it is less hard than quartz. It is very difficult to specify its precise hardness, as the same piece contains portions which, being iridescent, are naturally soft ; others of a milky whiteness, which are harder, and, lastly, others which surpass the rock crystal in resistance.
This substance, which has so many peculiarities, and is so specially prized for the pearl-white reflections which seem to move about inside the stone when it is turned,’ frequently owes more to the art of the lapidary for its admirable effects of light than to its natural beauty. In commerce it has a strange multiplicity of names ; now it is adularla, again it is lunaria or moonstone, sunstone, girasol, fish’s eye, water opal, or opal of Ceylon, according to the colours reflected.
From Siberia we have a special quality which is of a yellow colour, sprinkled over all the surface with an innumerable quantity of small golden spots, produced by very small crevices in the lamina. The most beautiful, cut invariably into smooth beads, have reflections in form of a star, diverging from the centre, but are very rare.
It is wrong to confuse this species of adularla with the Oriental aventurino, because, although it may have the same appearance, it has not similar hardness. The adularla from Ceylon is generally in larger pieces than that from St. Gothard, but it is not so bright.
The brilliancy and slightly bluish whiteness of the moonstone (lunaria) of Monte Stella are indescribable ; however, its value is diminished by certain oblique lines which cross it internally.
It does not appear that the ancients used this felspar, nor do I believe that it can be engraved. Caire, nevertheless, asserts that Plini had a head of Achilles engraved on a moon-stone by Grassi, and that it came out with extraordinary effects. He believes, however, that the ancient names of astrios, lapis specularis, and selenites, applied to this stone.
AQUAMARINA. AQUAMARINE
THIS stone is so named from its colour, which so much resembles sea-water. Like other gems, it is divided into Oriental and Western. Amongst those which, on account of their hardness, are called ” Oriental,” the most hard is merely a light blue corundum with a slight tint of green and yellow. It is easily known by its specific gravity, which is always above 4. This gem is very scarce, and it would have all the value of other corundums but for the colour which is common to a great number of other stones possessing little value.
The others are found in the Island of Ceylon, and from it they take their name. They are of a deeper greenish-blue colour, which renders them somewhat different from the Western stones. Their specific weight varies from 3.549 to 3.908, and it is thought that their hardness nearly equals that of the Brazilian chrysolite. They resist the wheel more than the others, and their brightness exceeds that of the Western gems. These are very transparent, and take a beautiful polish notwithstanding their inferior hardness, which is less than that of the topaz.
The specific weight is from 2.70 to 2.77. They possess double refraction, but in a weak degree. The cleavage is brilliant and wavy, sometimes scaly. Their primitive form is an elongated hexagonal prism. They melt when exposed to fire and lose their colour. They are found in Daouria, in the Uralian mountains, in Siberia, in the Altai mountains, and in America. When analysed they yield.. Those from Brazil are at present most prized because they are most beautiful.
The aquamarina of Saxony is a variety of quartz very little valued, and in that country it takes its name from the different stones whose colour it resembles; thus, the bluish is called aquamarina; the yellow, topaz ; and the olive, chrysolite. Great crystallizations of Western aquamarinas are found. That which was exhibited in London in the year 1855 was very beautiful.
Caire possessed one which weighed five hundred and forty carats. Fine and beautiful aquamarinas are worth from four to five hundred lire * the ounce ; those which are beautiful, but small, are valued at but twenty-five. The ancients used the aquamarina in its natural state, and also engraved, and they tell us of several celebrated intagli on that stone. They knew it under the generic name of aquamarina, and perhaps they often confused it with the beryllus, of which Pliny says, ” It has the same nature as the emerald, and is of a green colour.”
AMBER.
ALTHOUGH amber is not a stone, all writers place it amongst gems, as well for its value as that it has been used ornamentally by almost every nation of the earth, from the remotest period, and anterior to every historical record. Feuchtwanger asserts that the Phoenicians sailed to the Baltic for the sole purpose of procuring amber there. I am of opinion with Italian archaeologists, that the Tyrrhenians, long before the Phoenicians, had explored those seas, and drawn from the coasts in credible quantities of amber, with which they made ornaments of every kind and domestic utensils.
This is proved by the vases, cups, spindles, and other articles of unknown use, collected by me from the necropoli of the very ancient Pelasgic cities of Italy. The Tyrrhenians, and afterwards the Phoenicians, exchanged this substance with the Greeks, who named it electrum, ήλεκτρον. Homer says that the Trojan women wore necklaces of amber.
It seems that the electrical phenomena which this material exhibits were observed by the ancients, since Talete, as a result of his observations, came to the conclusion that amber was animated. Philemon and Pliny thought it a fossil ; and the latter person said, ” heat resuscitates amber.” Tacitus, having observed that it often contains insects, believed that it was a vegetable juice, and from this it derives the Latin name of succinum or sap.
People used it as an amulet, and it was administered as a drug.
Even in our own day many naturalists have considered amber a mineral ; but Sweigger and Brewster finally proved that it is a resinous gum ; that is, the fossil juice of a now extinct tree of the primeval period, called the amber tree.
This substance is found in round nodules, which vary from the size of a grape stone to that of a man’s head, and sometimes several of them are grouped together. When broken, one surface appears concave and the other convex ; it is translucent and transparent ; has single refraction, and resinous light. It is found in different gradations of colour, from greenish yellow to reddish yellow. It oxidizes in the course of years, and darkens into red, but its dust is always of a whitish yellow.
It scratches chalk, but is scratched by carbonate of lime. This substance, under the action of the blow-pipe, burns with a yellow or bluish-green flame, emitting a dense smoke having a pleasing smell, and leaving a carbonized residue. Warm oil bends and makes it pliable, but it does not melt so soon as other gums, as it requires the heat of 517° Fahrenheit.
By distillation it produces an acid, which from its name is called acido guccinico, and an essential oil named oil of amber ; whilst in the retort there remains a brown deposit, known as amber resin, which is used as a varnish. Insoluble in water, it dissolves in alcohol, as also in a solution of subcarbonate of potass.
Its component parts are carbon, hydrogen, and oxygen, with lime, alumina, and silex. Of a specific weight varying from 1.080 to 1·08ο, its power of refraction is from 1.365. Mixed with drying oil of linseed and essence of turpentine, it makes another excellent varnish.
Amber is found thrown from the sea on the shore. It is gathered in great abundance by the fishermen on the Prussian coasts, after the autumnal tempests of the Baltic. It is also found in China and America; in small quantities in Sicily ; and in Catania a very singular kind, of a bluish colour. Even in France some is found.
In Prussia, however, there exist numerous caves of amber, which are explored by practised miners at a depth often of more than one hundred feet. The amber of the mines differs from that of the waters only in being more brittle, and it is often covered with a thick crust of clay.
Those ambers which contain insects take the name of insectiferous amber. The yellow amber cut in the form of beads, either smooth or in facets, is much used both in the East and West as a feminine adornment. In the East it is called Karabè, and used to ornament pipes, pistols, guns, daggers, and yataghans.