Diamonds are usually found in alluvial deposits derived from the materials brought down from the hills bordering the higher parts of the valleys. They are generally associated with a large assortment of rocks, minerals, and gems, as quartz, diorite, mica-schist, gold, platinum, calcedony, kyanite, red hematite, magnetic iron, rutile, chrysolite, tourmaline, topaz, etc., and sometimes with the black and opaque carbonado, and crystalline concretions of translucent diamond useless for cutting. In Brazil the gravel or conglomerate is termed cascalhao; when consisting of broken quartz, gurgulho. Rarely has the diamond been found in the original matrix, but it is stated to occur in hornblende slate, and in a flexible sandstone, named itacolumite, from the Pic d'Itacolumi, in Brazil. Diamonds are received in large numbers from Brazil, where they were first noticed in the early part of the 18th century, as stones found in the gold washings of the elevated districts of the Cerro Frio, and about the sources of the Jaquetinhona, San Francisco, etc. They were used as counters in card playing by the gold-miners until their real value was inferred by a person who had seen similar stones in the East Indies.

According to Mr. Martin, Minas Geraes is the most productive of the Brazilian mines; the diamonds have a dull, frosted coat, and with a more or less greenish hue. Sincora, in the province of Bahia, discovered about 1843, was very productive for five or six years, yielding in the first two years diamonds valued above half a million of money; they are generally of a yellow and brown tinge, but sound, with a bright coating; they lose little in cutting, and are associated with the black and opaque carbonado. Bugagum, more recently discovered, yields crystals of a milky white, pure white, and light brown colour, generally distorted, and resembling in some respects the Cape diamonds; the "Star of the South" was found here. Cuiaba yields very few stones, but in character they are like those of Sincora, and form the best points for glaziers' diamonds. It is estimated, since the opening of the Brazilian mines, they have yielded altogether two tons of diamonds.

The quality and perfection of diamonds depends upon transparency, colour, freedom from specks, cavities, and flaws. Their value, up to a certain size, is estimated by their weight in carats (the carat being about 3 grains troy); but the value also depends on their purity, so that it may vary from £8 to £12 a carat. When a diamond weighs more than one carat its value in pounds sterling is found by multiplying the square of the weight in carats by 10 or 12, according to the general brilliancy and form of the stone.

Among the most remarkable diamonds are the Mattan, 367 carats; Great Mogul, 279%; Russian, 195; Austrian, 139; Regent, 136; Sanci, 106; Star of the South, 125; Nassac, 78; Koh-i-Noor, 1021. The great diamond called the "Star of South Africa," brought recently from the Cape, weighed 83 carats before cutting, and has yielded a stone of great beauty, weighing 46

carats.*

• We are indebted to Prof. Tennant for the engravings representing this fine diamond.

Ruby, Sapphire, and other varieties of Corundum.-The next important mineral gems after the diamond are the transparent and coloured varieties of corundum, which consist essentially of alumina, or oxide of aluminium, and to which, from their hardness and brilliancy, the term precious was formerly restricted. According to their colour they have received various names; the indigo, or pale blue variety, is the oriental sapphire; the cochineal red, the oriental ruby; the yellow, the oriental topaz; and the violet, the oriental amethyst. Besides these there is the asteria, or star sapphire, which has a chatoyant appearance. Sapphires vary much in quality and value, according to their colour, those of the rich velvet-blue being of the most value. When the ruby attains the size of 5 or 6 carats it is considered of far higher value than a diamond of the same weight, and is more highly esteemed. Besides the transparent varieties of alumina, there is the translucent and cleavable one, known as corundum, which is largely used for grinding glass and other substances. With shellac it forms the material of which dentists' files are made. The granular impure corundum constitutes emery, which is extensively used for various purposes of polishing, when reduced to coarse powder by stamping. Besides being cut as gems, sapphires and rubies are largely used for the balance holes in watches, and are prepared for this purpose at Geneva, at a less cost than in London. The best rubies chiefly come from Ava and Pegu; the sapphires from Ceylon, as least those which are used for jewellery. The finest stones occur usually in the beds of rivers, although they are also found in various crystalline rocks. Corundum is obtained from the Mysore district, from Ava and Malabar; and the more impure variety, emery, from Asia Minor, the Greek islands Samos and Naxos, and from Chester county, Massachusetts, associated with diaspore, magnetite, etc. Sapphire crystallises in modified hexagonal prisms, and is next in hardness to the diamond.

Partly allied to sapphire in composition is spinel, which is composed of alumina and magnesia, coloured either by iron or chromium. When of fine colour it is a valuable stone; the deep red is the spinel ruby, the pink variety is the Balais ruby, the yellow is the rubicelle, and of violet colour the almandine. Spinels are chiefly derived from Ceylon, where they are found in alluvial deposits. Like the true rubies, they are largely used in jewelling watches, both in this country and Switzerland. Spinel is sometimes of neutral blue tint, and is then highly prized. The spinel differs from the oriental ruby in colour and in crystalline form, which is a regular octohedron, sometimes macled; also in being less hard, and in having a lower specific gravity. The latter character distinguishes it from garnet, but is superior in hardness to that gem.

It is

The Chrysoberyl is an aluminate of glucina, and approaches the sapphire in hardness and specific gravity, but is distinguished from it by its crystalline form and colour, the latter being pale yellow, or one of various shades of green. frequently used in jewellery, also for drilling holes in porcelain and glass. Some varieties are sold at a very high price, and are called oriental chrysolites. These stones occur as rolled pebbles in Brazil, where they are highly esteemed, and in Ceylon; and the common ones in the United States and Moravia. Cymophane is an opalescent variety, generally cut en cabochon, like the carbuncle.

Beryl, Aqua Marine, and Emerald.-These important gems crystallise in hexagonal prisms, with the sides striated longitudinally, and are thus distinguished from rock crystal, which has transverse striæ. They are composed of silicates of alumina and the rare earth glucina, which is only found in a few other minerals, as in phenacite and euclase, which last receives a high polish, but from its brittleness is useless as an ornamental stone. The emerald is deep green, and the aqua marine pale bluish green. They are only used for jewellery, and are less hard and have a lower specific gravity than sapphire. The finest emeralds are from Muso, New Granada, whence they were brought about 15 years since, but where they have now become scarce. Emeralds of lower quality are found in Siberia, the Tyrol, and Norway. Emeralds were

frequently used as decorative ornaments for their deities by the Incas, Aztecs, and other peoples of Central America. The beryl is, however, much more abundant, and when transparent is termed aqua marine. The finest beryls are from Siberia, Madras, and Brazil; the less transparent varieties are of no great value, but occur in masses of large dimensions in many localities of the United States, some weighing more than 4 or 5 tons. In this country the beryl is found in granitic rocks with topaz at Lundy Isle, in the Mourne Mountains, and abundantly at Donegal, also at Limoges, in France.

The Topaz is a fluo-silicate of alumina, crystallising in rhombic prisms with striated sides; it has a basal cleavage, and is rendered very electric by friction. The chief supply of topazes for the purpose of jewellery come from Brazil. These stones are generally of yellowish brown colour, sometimes of a pale blue, as those from Brazil and Siberia, where the topaz attains several pounds weight. Topaz is very abundant, chiefly in veins in granite, and sometimes forms a massive rock called topazfels, as in Saxony; it is found in Cornwall, Ireland, and Scotland. The white varieties are generally found as rolled pebbles, at Minas Novas, Brazil; and at Flinders Island, Tasmania. The colour of the pink topaz is produced artificially by exposing the stone to a low red heat.

The Garnet Group is of next importance, and includes gems that are obtained in great abundance, being widely distributed, and found in granite, many metamorphic rocks, and also in alluvial deposits, where they occur generally transparent; while in the matrix the majority are translucent and opaque. Mineralogists distinguish three principal kinds of garnet-the iron, alumina, and chrome garnet. The crystalline form of the garnet is a modified dodecahedron; its hardness is less than that of quartz, but its specific gravity is higher. The varieties most used are the violet coloured almandine, or precious garnet, from Ceylon and Pegu, and the brownish red, or carbuncle, usually cut en cabochon. The cinnamon stone, or essonite, commonly known as the jacinth, or hyacinth, is the yellowish brown variety, and is chiefly obtained from Ceylon; the pyrope, or Bohemian garnet, is also used as a gem. The garnet is largely used for jewelling some kinds of watches made in this country and in Switzerland; and the common garnet is sometimes used for polishing, and as a flux. Zircon, Hyacinth, and Fargoon are silicates of zirconia, crystallising in square prisms, and have the greatest density of all the precious stones, being 4.6. They vary in colour from an orange or reddish brown (hyacinth) to a dark olive green, and have a lustre almost equalling the diamond, of which they were formerly considered varieties. Zircons occur embedded in granite, syenite, basalt, lava, and are found in alluvial beds in Ceylon. The green coloured variety, under the name of jargoon, is found in Ceylon. These stones are frequently sold as inferior diamonds, the colour being partially removed by heat, and the density being increased after heating, as shown by Prof. A. Church. The Peridot, or Chrysolite, differs both physically and chemically from chrysoberyl, or oriental chrysolite, by its inferior degree of hardness, and in being a silicate of magnesia. Although of a soft green colour, it is seldom used in jewellery. It is brought over from the Levant, but the exact locality of its occurrence is unknown. The common variety, the olivine, is very abundant in eruptive rocks.

Ornamental Varieties of Silica.-Of the pure siliceous minerals used as ornamental stones, there are, in the first place, the crystallised transparent forms of silica, as rock crystal, amethyst, the violet quartz, cairngorm or false topaz, and the yellow or brown quartz; secondly, there are the amorphous translucent and opaque kinds, as chalcedony, agate, onyx, sardonyx, cornelian, chrysoprase, heliotrope, jasper, and the hydrated silica known as opal. The latter owes its peculiar play of colour to the numerous irregular sized fissures traversing it; these contain lamina of air, which reflect the rays of different colours and intensity. Some of the finest opal comes from Hungary, Mexico, Honduras, etc., where it occurs in igneous and other rocks.

Rock crystal is also known as Bristol, Welsh, Cornish, and Irish diamonds, and has occasionally been mistaken for the true diamond; it is readily distinguished from the latter by its crystalline form (a six-sided prism), its imperfect cleavage, and its inferior hardness, specific gravity, and lustre, most of which characters also distinguish the amethyst from the oriental amethyst, or sapphire, and the cairngorm from the true topaz. The finest amethysts come from Brazil and Ceylon, but they are found of some beauty in Cornwall and Ireland. Besides being known abroad as the "Bishop's stone," many virtues have been attributed to the amethyst, among others one to which it owes its name, that of preventing intoxication.

Chalcedony, agates, and other translucent forms of quartz, chiefly occur as nodular masses in cavities of rocks. Agates, or the banded forms, are found in igneous and other rocks in many localities, as Brazil, India, Scotland, and Oberstein, at which latter place they are largely worked, and exported to various parts of Europe, and in this country are sometimes called Isle of Wight and Brighton pebbles. They are coloured artificially-black, brown, red, blue, and green-by certain chemical processes, and present alternate bands of colour, due to the greater or less absorbing powers of the different layers of the agate. Quartz, either fibrous or with some enclosed foreign fibrous body, constitutes the cat's-eye, which has a chatoyant lustre. The term avanturine is applied to quartz and felspar, with numerous small parallel cracks, or disseminated particles of some substance, as mica, etc. Other enclosed substances, as micaceous iron, asbestus, oxides of titanium and manganese, give to rock crystal the names of rubasse, Cupid's nets, arrows, or pencils, and Venus's hair-stones.

Tourmaline is occasionally used for decoration, as it resembles in colour many of the gems, and has often been sold for them, but is not so hard. Its chief value is due to its optical properties in connection with the phenomenon of polarisation of light. It is a boro-silicate, with alumina, iron, magnesia, and fluorine, is chiefly found in granitic rocks, crystallises in hexagonal prisms, is electric when heated, and is of brown, green, blue, black, and red colours. The blue is called Brazilian sapphire, the yellow is the Ceylon peridot, and the green the emerald of Brazil, where it is highly esteemed by the clergy; the red variety, or rubellite, from Ava and Siberia, is a valuable stone, and is cut en cabochon, like carbuncle.

Disthene, or kyanite, a silicate of alumina, of an opalescent sky-blue, has sometimes been used for oriental sapphire, but differs from it in hardness, specific gravity, and its easy cleavage.

Moon-stone, sun-stone, amazon-stone, and avanturine, are forms of felspar (a silicate of alumina and alkalies) which owe their value as ornamental stones to certain effects of light produced by their colour, structure, and other physical characters.

The last ornamental stones of any importance are generally compact, amorphous, and opaque, of blue, green, or bluish-green colours. Two of them are comparatively soft-malachite and lapis lazuli; while turquoise equals felspar in hardness. Malachite is a carbonate of copper, and fine specimens are obtained from Siberia and Australia. Lapis lazuli is of an azure blue, and consists of silica, alumina, lime, soda, and sulphur; it is found mostly in altered rock, in Persia, China, and Siberia, and was formerly the source of the beautiful pigment ultramarine, which is now, however, artificially prepared. Turquoise is a phosphate and a hydrate of alumina, coloured by copper; it occurs in small reniform masses, of sky-blue colour, in Persia, where it is highlyesteemed, and at Wady Maghara, in Arabia Petræa, where it occurs lining the joints, in a mottled quartsoze sandstone, or a short distance from them. bone turquoise, or odontolite, formerly used in jewellery, is fossil bone or teeth, coloured by phosphate of iron.

The

The following table indicates the colours, the degree of hardness, the specific

gravity, and the kind of refraction (single or double), characterising each of the principal gems referred to by the Lecturer :

Specific

Colourless. Red. Yellow. Green. Blue. Violet, Brown. Black. Hardness. Gravity. Refraction.

[This full account of Prof. Morris's Lectures is based upon the excellent reports printed in recent supplements to the Mining Journal.]

VARIA.

St. Paul's Cathedral.-Professor Lightfoot, of Cambridge, has been appointed to the vacant canonry at St. Paul's.-The Company of Dyers have subscribed twenty-five guineas, and the Company of Pewterers ten guineas, towards the fund being raised for the completion of the interior of the cathedral. Eighteen of the City Companies have now subscribed to this national work.

Miss Garrett, M.D., was married to Mr. James George Skelton Anderson, at the English Presbyterian Church, Marylebone, on the 9th ult.

The Mercers' Company.-A grant of ten guineas has been made by this Company to the funds of St. Peter's Hospital, Berners-street.

People's Edition of Thomas Carlyle's Works. The first volume of this new edition of Carlyle's writings will be issued during the present month. Sartor Resartus, handsomely printed in one compact volume, with a portrait of the author, will be a remarkable two-shilling book.

Obituary. On January 26, at Boston, in the United States, George Ticknor, the historian, died at the advanced age of 80. The New York Times says "he was probably the most thorough literary scholar which this country has ever produced."-On January 31 died Mr. William Hayes, Senior Conveyancing Counsel of the Court of Chancery. His contributions to the literature of his profession are numerous and important.-On February 3, Baron Joseph Eötvös, the Magyar patriot, died in the 58th year of his age.-On February 9, the Rev. Henry Melville, canon of St. Paul's, died in his 73rd year.—On February 12, died Mr. John Greenwood, Q.C., Solicitor to the Treasury, widely known as a conscientious and valuable public servant.-On February 14, Mr. James Sidebottom, M. P., died at his residence, Acres Bank, Staleybridge, aged 46.– On February 24, at Clapham Common, after a long illness, died Elizabeth, the beloved wife of J. P. Gassiot, D.C.L., F.R.S., Vice-President of this Institution.

Our First Librarian.-Under the head of "Popular Errors," in the Athenæum of last Saturday, S. D. writes :-"The biographers of Prof. Porson commonly state that his father was a weaver by trade, and that the son was also put to the loom. This is wholly incorrect. The father was not a weaver.