First Floor.
Gallery of Minerals.
The gallery on this floor, entered from the south end of the east corridor of the hall, contains the extensive Mineral collections, a fuller description of which will be found in special guides.[21]
Introductory Collections.
Entering the gallery the visitor will find, in the first window-case on the left-hand side, a series of specimens selected and labelled to serve as an introduction to the study of Minerals. Beginning with a definition of what is meant by a Mineral, it shows how essential characters were gradually recognised, and how Minerals are distributed into kinds and classified. In the next three window-cases specimens are arranged to illustrate the characters of Minerals and the various terms used in their description.
Rocks.
In the remaining six window-cases on the same side of the gallery, a corresponding series of specimens illustrative of the characters and classification of Rocks is exhibited; and the eleven window-cases on the opposite side contain a collection illustrating the various kinds of Rocks.[22]
General Collection of Minerals.
In the table-cases of the gallery are exhibited specimens of every important Mineral species and variety preserved in the Museum. The cases containing this general collection are numbered from 1 to 41, and the eight panes of each case are severally distinguished by the letters a to h. For the use of the student there is published an Index to the names of all the numerous Mineral species and varieties represented in the collection, with references to the table-cases in which the specimens are placed.[23]
The system of classification, which includes not only ores, but all known Minerals, is not easy for the visitor to follow, and it is therefore convenient to indicate the positions in the gallery of those minerals—as, for instance, precious and ornamental stones, and metallic ores—which have an interest for all; for details, reference must be made to the Mineral Guide. Most of these Minerals occur as crystals, the forms of which can be referred to six systems of crystallisation.
Fig. 58.—The Colenso Diamond, from South Africa. Natural size.
Native Elements.
I. In cases 1 and 2 are the native metals, as Copper, Silver, Gold, and Platinum; and non-metals, as Sulphur, Diamond, and Graphite. The large symmetrical South African “Colenso” Diamond ([fig. 58]), weighing 130 carats, presented by the late Professor John Ruskin, is worthy of special attention (case 1f). Models of some famous diamonds, including “The Cullinan Diamond,” the largest ever found (weight before being cut, 3025¾ carats, or about 1⅓ lb. av.) are exhibited.
Sulphides.
II. The next six cases contain Minerals which have mostly a metallic lustre and consist of metals in chemical combination with elements of the Sulphur or Arsenic groups.
Argentite (3d) is an important Silver-ore, containing 87 per cent. of Silver and 13 of Sulphur.
Blende (4b) is a valuable Zinc-ore, and contains 67 per cent. of Zinc and 33 per cent. of Sulphur.
Galena (4e) is by far the most important ore of Lead (Lead 87, Sulphur 13, per cent.).
Copper-glance (3e) is a common ore of Copper (Copper 80, Sulphur 20, per cent.).
Cinnabar (3h) is the ore from which Mercury or Quicksilver is obtained (Mercury 86, Sulphur 14, per cent.).
Pyrites (5d), one of the most common of Minerals, is a compound of Iron and Sulphur (Iron 47, Sulphur 53, per cent.).
Erubescite (5e), Copper pyrites (5f), and Tetrahedrite, or Grey Copper-ore (7a), are valuable sources of Copper.
Chlorides, etc.
III. Common Salt, the chloride of the metal Sodium, is exhibited in case 8f, and Fluor-spar, a fluoride of Calcium belonging to the same division, begins at case 7e.
Oxides.
IV. The next division consists of compounds of Oxygen and includes most of the stony Minerals.
Cuprite (10a), an important ore of Copper (Copper 89, Oxygen 11, per cent.), is at first ruby-red in colour, but becomes blackened by exposure to light.
Spinel (10e), in its transparent varieties, is one of the precious stones; the deep red being the Spinel Ruby (less dense and less hard than the true Ruby), the rose-tinted the Balas Ruby, and the yellow or orange-red the Rubicelle of the jewellers: sometimes, it has a dark blue colour. On account of their hardness, the less valuable specimens are used for the jewelling of watches.
Magnetite, or Magnetic Iron-ore (10f), the richest ore of Iron, of which it contains 72 per cent., is the natural magnet.
Uraninite, or Pitchblende (10h), consists mainly of Uranium and Oxygen, but contains traces of Helium and Radium, of which latter it is the commercial source.
Chrysoberyl (9e) is another precious stone, almost equal in lustre and hardness to the Sapphire; one variety is a beautiful greenish-yellow; another, with a peculiar play of light, is the Cat’s-eye; and a third, green by sunlight, but red by candle- or lamp-light, is known as Alexandrite.
Corundum (9f), when clear and of the proper colour, is, after the Diamond, the most precious of stones. When pure, it is colourless, but with minute traces of colouring ingredient it assumes the richest and most varied hues; when red it is Ruby, and when blue Sapphire; the yellow, green, and purple varieties were at one time known respectively as the Oriental Topaz, Emerald, and Amethyst. The prefix “Oriental” was at first used to suggest that the stones are not ordinary Topaz, Emerald, and Amethyst, but other similarly coloured minerals coming from the East (India, Ceylon, Siam, Pegu, etc.); it was afterwards understood to suggest only the excellence of their characters. The Star-stone, another variety of Corundum, when placed in a strong light shows a six-rayed star.
Hæmatite (11a) is a valuable ore of iron (Iron 70, Oxygen 30, per cent.).
Cassiterite, or Tin-stone (11f), is the ore of Tin, of which metal it contains 79 per cent.
Zircon (13b), when clear and without flaws, is one of the precious stones: one variety with peculiar red tints is the Hyacinth or Jacynth, while the colourless, yellowish, and dull green phases are termed Jargoon: the colourless variety, owing to its high refractive and dispersive power, approaches the Diamond in brilliancy.
Quartz, which is Silica, the oxide of Silicon, is the most common of Minerals. In its clear and transparent variety it is the Crystal of the ancients and the Rock-Crystal of modern times; it is the Brazilian Pebble of spectacle-makers (14c). After the clear come the smoky varieties, including the Scotch Cairngorm and Occidental Topaz (14g). Next follows the Amethyst (14g), one of the less valuable, though one of the most beautiful, of gem stones. The Quartz Cat’s-eye (13f) is a variety presenting a similar play of light to that of the Chrysoberyl Cat’s-eye already referred to: the effect is due to enclosed fibres of an Asbestos-like mineral in the specimens from Ceylon, and to fibres of Crocidolite in the blue, and of altered Crocidolite in the brownish-yellow specimens from South Africa.
Jasper (13g) is a coloured mixture of Silica and Clay, distinguished from ordinary Quartz by its opacity and dull earthy fracture. It is of various colours, chiefly red, brown, yellow, and green; the colours being arranged sometimes in a nodular form, as in Egyptian Jasper, at other times in stripes, as in Riband Jasper.
The Lydian or Touch-stone (15a), by reason of its hardness and black colour, has been used from remote ages to test the purity of precious metals.
Hornstone (15a) is a variety of Silica without evident crystallisation, and generally presenting a more or less splintery fracture; in one kind, Flint (15b), the surface of fracture is generally shell-shaped (conchoidal), sometimes conical, as is well shown by specimens in the case.
Chalcedony (15b), which has a lustre nearly that of wax, is translucent. The specimens of Enhydros from Uruguay (15d) are of especial interest as containing imprisoned water.
Heliotrope, or Bloodstone (16a), is a green stone with red, blood-like spots.
Next follow the Plasma and Chrysoprase, which are green stones: and the Sard, generally brownish-red; as also the Sardonyx, its banded variety. All were much prized by the ancients because, though hard and tough enough to resist ordinary wear and tear, they are more suited to the display of the engraver’s skill than the still harder and more precious stones.
Then come the Agates (16b), chiefly formed of thin layers of porous Chalcedony of different colours, though the material of many of the white layers is a compact Semi-opal. Most are now brought from Uruguay, in South America, and cut and polished at Oberstein, in Germany, where in former times Agates were collected in quantity from the mountains of the district. Sometimes the layers are parallel, and the stone is then an Onyx, useful as a material for cameos: or the bands of a section are arranged in parallel sets of zigzag lines, and the stone is then called a Fortification-agate; but in the ordinary agate the layers are variously curved. Moss-agates, or Mocha-stones (16e), are varieties of Chalcedony enclosing moss-like forms of oxides of Manganese and Iron, and green earthy Chlorite. Carnelian (16e) is a beautiful red stone much valued by the engraver: its fracture has a peculiar waxy lustre, and is distinct from that of the Sard, which is dull and horn-like.
Opal, including the Precious or Noble Opal (16f), among the specimens of which is a fine suite from Queensland presented by the late Professor Story-Maskelyne, is hydrated Silica.
Carbonates.
Witherite, the carbonate of Barium (18a), is used in the manufacture of plate-glass. Strontianite (18b), the carbonate of Strontium, is one of two minerals from which Strontium nitrate is made for use in the manufacture of fireworks, owing to the fine crimson colour which the salt gives to the flame: the Strontium minerals are also employed in connection with sugar-refining. Cerussite (18b) is the corresponding carbonate of Lead, and when abundant is a valuable ore of that metal.
Calcite (18e), a carbonate of the metal Calcium, is represented by a fine suite of specimens, illustrating an almost endless variety of crystalline form. The clear variety from Iceland is largely used in optical instruments for polarising light. Chalybite, or Spathic Iron-ore (20h), is the carbonate of Iron, and a valuable ore of that metal. The most important English Iron-ore, Clay Ironstone, is a mixture of Chalybite and Clay. Calamine (19h), a carbonate of Zinc, is an important Zinc-ore. Chessylite (21d) and Malachite (22b) are respectively the blue and green carbonates of Copper, and are used as ores of that metal. Malachite is found in large masses; by reason of the high polish which it takes and its beautiful markings, it is much used for ornamental work of various kinds.
Silicates.
Passing to the Silicates, we come to Olivine (22f), one of the less hard of the precious stones; when of a yellow colour it is known as Chrysolite, while the green variety is the Peridot of jewellers. Hiddenite (23a) is a rare emerald-green variety of Spodumene, and Kunzite is a lilac-coloured variety which is used as a gem stone.
Asbestos (24c), a kind of Hornblende (a mineral common in rocks of igneous origin), is found in long fibres; in some of its varieties it is so flexible that it can be woven into gloves and other articles. The term Asbestos, meaning unquenched or unquenchable, was applied by the ancient Greeks, because, owing to being unaltered by heat, wicks made of this mineral were used in maintaining the perpetual sacred fires of their temples. Napkins of Asbestos were cleaned by being thrown into the fire; Asbestos-cloth was also used in the process of cremation to keep the ashes of the body distinct from those of the fuel. It is now employed for lining iron-safes, packing for steam-pipes and boilers, and in gas-stoves, for which purposes its low conductivity for heat renders it serviceable.
Jade or Nephrite (24d), a valued mineral, belongs to the same group as Hornblende. The various shades of colour and the beautiful polish which this tough mineral will take are illustrated by specimens in the case. Several worked specimens from New Zealand and China are exhibited. An immense water-worn mass, weighing 1156 lb., found some years ago in Asiatic Russia, is mounted on a separate stand near by.
Meerschaum (23g), the light soft porous mineral used for tobacco-pipes, is a hydrated silicate of Magnesium. Serpentine (25a) is another hydrated Magnesium-silicate: the ease with which it is worked and polished, its green colour, and varied markings render it much sought after as a material for mantel-pieces, tables, and other indoor work: exposed to the weather it soon loses its polish.
Topaz (25c) in its clear varieties is one of the precious stones. The crystals from the Urulga river, Siberia, are remarkably fine, and of a delicate brown colour; they are kept covered, as the action of light slowly bleaches them. The yellow crystals from Brazil assume a peculiar pink colour when heated, and are then known to jewellers as Burnt or Pink Topaz. A fine orange-red crystal from Brazil is exhibited.
Garnet also belongs to the group of precious stones; when the red is tinged with violet, the stone is the Almandine or Syrian Garnet (named after Syriam in Pegu), and when cut en cabochon, the Carbuncle of jewellery (26f); the Cinnamon-stone or Hessonite varies in tint from hyacinth-red to honey-yellow (26e); the Pyrope, including the “Cape Ruby” and the Bohemian garnet, is blood-red (26e), Demantoid is an emerald-green (26g).
Jadeite (27a) is one of the green stones which, under the name of Jade, are wrought into ornaments in China: from jade it is distinguished by its chemical composition, structure, and higher specific gravity. Among the specimens of Epidote (27c) a remarkable series from the Untersulzbachthal, Austria, is exhibited.
Mica (28a) is the name given to a group of minerals differing much from each other in chemical composition and optical properties, but having as a common character an easy splitting, or cleavage, in a single direction, and thus affording plates remarkably thin, transparent, tough, and elastic. One of these minerals, Muscovite (28d), has been used in Russia in place of glass for windows, and is now in common use for lanterns and stoves, not being so easily cracked as glass by changes of temperature; it is often known in commerce as talc, a term restricted by mineralogists to a different mineral.
The group of Felspars, the most important of the rock-forming minerals, begins at case 28f. After the Felspars comes Beryl, of which the bright green variety, Emerald (29c), is one of the most valued of precious stones. It was in ancient times worked in Egypt, as is proved by specimens found in the old workings by Sir Gardner Wilkinson, and presented by him to the Museum. Emeralds occur in the Urals; but the locality for the finest stones has long been Muzo, about seventy miles from Santa Fé de Bogotá, in South America. Faceted specimens of the colourless Beryl, of the bluish-green Beryl, known in jewellery as Aquamarine, and of pink Beryl from California and Madagascar, are exhibited (30a).
In cases 30f to 32d will be found examples of the Zeolite group of minerals.
Tourmaline (33a), when free from flaws, is, in some of its varieties, to be classed with the precious stones; among these being a pink variety called Rubellite. Fine specimens of Rubellite from Burma, the Urals, and Madagascar, are shown in the case; one specimen from Burma, poor in colour but remarkable for its size and shape, was brought home by Colonel Symes, to whom it had been presented by the King of Ava in the year 1795. The pink-and-green tourmalines from Maine, U.S.A., and the magnificent crystals from San Diego Co., California, are among the more beautiful of the mineral products of the United States. Examples of the blue Tourmaline, or Indicolite, are shown in case 33b.
A rich blue mineral, the Lapis-lazuli of jewellery (34b), brought from Persia, Siberia, Bokhara, and Chili, is a mixture of various species. When powdered, Lapis-lazuli furnished the once costly pigment ultramarine; but by the discovery of a method of producing an artificial and cheap form of the latter, the use of the mineral as a pigment has ceased.
Sulphates, Phosphates, etc.
The sulphates of Strontium, Celestite (35c), of Barium, Barytes or Heavy Spar (36a), and of Lead, Anglesite (36e), are all represented by series of specimens.
Gypsum, or Selenite (36f), is a hydrated sulphate of the metal Calcium: when heated, it gives up its water of crystallisation and falls to a white powder, known as “Plaster of Paris,” which, when moistened, again combines with water and yields a coherent solid. Gypseous Alabaster, a massive variety of Gypsum (36h), owing to its whiteness, fine texture, and softness is used as a material for statuettes and other indoor ornaments. Oriental Alabaster is a harder substance, Stalagmitic Calcite, carbonate of Calcium.
Borax (37c), a borate of Sodium, is much used as a flux, also in soldering, and in the preparation of easily fusible enamels. It was formerly carried over the Himalayas on sheep and goats from lakes in Tibet, but is now obtained largely from the Borax-lakes of the United States, and is also extensively prepared from the boracic acid lagoons in Tuscany.
Nitratine or Soda-nitre (37d), found in Chili in beds of large extent, is largely used for the preparation of Nitric Acid and Saltpetre, and is also used as a fertiliser.
Calaite or Turquoise (38g), a phosphate of the metals Aluminium and Copper, is generally massive; only very rarely does it occur in the crystalline state. Being as hard as Felspar and taking a good polish, it has been much prized in jewellery; that which comes into the market is chiefly brought from the Turquoise-mines not far from Nishapur, in Persia.
Amber.
As a supplement to the collection of simple Minerals, is arranged, in case 41, a group of natural substances which either belong or are closely related to the Mineral Kingdom, although, in the formation of most, organised matter has played a very important part. The most important of these are Coal and Amber. Coal (41a), in most of its varieties, gives structural evidence of its vegetable origin: its chemical composition depends on the amount of change which has taken place, and thus is less definite than in the preceding minerals. In the variety called Anthracite all traces of the original organised structure have disappeared. Amber (41c), in ancient times regarded as one of the precious stones, is likewise of vegetable origin. It is fossil resin, chiefly derived from trees allied to the pines; its originally sticky condition is proved by the insects sometimes found enclosed.
Larger Mineral Specimens.
In the pavilion at the east end of the gallery the visitor will find many mineral specimens which, owing to their size, cannot be satisfactorily exhibited in the table-cases.
Among these, attention may be directed to the magnificent series of Minerals in the wall-cases, and to the large specimen of Gypsum, or Selenite, presented by H.R.H. the late Prince Consort, which, with some fine masses of Iceland Spar, is exhibited in a special case.
Of the four table-cases in the windows of the pavilion, the first three contain a series illustrating the various kinds of Pseudomorphs, or minerals in which the original constituent has been altered and replaced by a new substance which preserves the crystalline form of the first. The fourth displays a set of specimens selected by the late Professor Ruskin to illustrate varieties of Silica.[24]
Meteorites.
The most important feature of the pavilion is the collection of Meteorites,[25] of which the smaller specimens are shown in the four central cases. The fall of masses of stone and iron from the sky, though observed again and again since the most remote ages, was very rarely credited by anyone beside the spectators themselves; and till the beginning of the nineteenth century no attempt was made to collect such specimens for examination and comparison. In the special guide it is shown how evidence of the actual fall of such bodies at length became irresistible, and a description is given of the circumstances attending their fall, of their general characters, and their chemical composition: illustrative specimens, collected together for easy reference, will be found in one of the cases. It is also shown that meteorites are closely related, not only to shooting stars, but also to comets, and probably to nebulæ and fixed stars.