Of Sulphur, large and splendid yellow crystals are exhibited from Div. 1. Conil, near Cadiz, and fine specimens from Sicily. The glazed front Case 4. of Case 2 contains specimens belonging to this division, of extraordinary size and beauty.

DIVISION II. COMPOUNDS OF THE ARSENOID AND THIONID ELEMENTS. DIV. II. Cases 4 (ii.) Leaving the native elements, we enter upon minerals which are the to 10 (i.) products of the chemical combination of the elements with each other; but the transition is not an abrupt one. The alloys, or mixtures of metals of one and the same group, were associated in the first division with the metallic elements that compose them. But where metals belonging to distinct chemical groups are combined, they cannot be classed with the free elements. Such are the combinations of Arsenic, Antimony, and Bismuth with metals of other groups, and they (the arsenides, antimonides, &c.) accordingly take their places as the first section of Division II and will be found arranged in the latter half of Case 4.

Next in order to these are placed, as a second section of Division II., the compounds of metals with the "thionid elements;" and accordingly the tellurides, selenides, and sulphides are displayed in Cases 5 to 9 inclusive.

These are succeeded by a third section of this division, namely, by Minerals to form which compounds belonging to each of the former sections are combined together.

These three sections may be severally represented by their prominent members, the arsenides, the sulphides, and the arseno-sulphides.

66

The first of these sections comprises the cuprous arsenides, such Section i as Domeykite, the tricuprous arsenide; also, the antimonide of Case 4 (ii.) Silver or Dyscrasite, diargentous antimonide. Besides these there are included in this section several compounds of Iron, Cobalt, and Nickel. Nickeline, called also "Copper-Nickel," from its colour, is a rhombohedral mineral, the nickel arsenide. Chloanthite is the nickel diarsenide and Smaltine, or tin-white Cobalt," the cobalt diarsenide, of which Safflorite is a variety, containing Iron in place of a part of its Cobalt. These minerals are cubic in crystallisation, but some of the substances which constitute them are also found in orthorhombic forms, affording examples of dimorphism. Thus the nickel diarsenide, when thus occurring in crystals of the orthorhombic system, is the mineral Rammelsbergite (of Dana), and Leucopyrite is a corresponding iron diarsenide.

In this section is also included the cobalt triarsenide, Skutterudite. The second section includes the various compounds of Sulphur. Section ii. Selenium, or Tellurium-the Thionid elements-with the metals, Silver, a monad element, and Copper, a metal that in one group of its salts plays the part of a monad element, contribute to form a small group in this section of the type M, E. Eucairite is a selenide of Silver and Copper, and Crookesite is a selenide of Copper and Thallium.

DIV. II.
Case 5 (i.)

Hessite and Petzite are the tellurides of Gold and Silver, Naumannite the corresponding selenide of Silver, while Argentite is the sulphide of Silver. The latter are cubic in crystallisation, but the silver sulphide is a dimorphous mineral presenting itself as Acanthite in forms belonging to the orthorhombic system. To this system belongs also Copperglance, a valuable ore of Copper, the "cuprous" sulphide. Among the Case 7 (i.) other important minerals in this section, a cubic series of monosulphides occurs which includes two commercially very important Cases 5 (ii.) ores-Galena, the sulphide of lead, and Blende, the sulphide of zinc. A Rhombohedral series includes Covelline, the cupric sulphide, Cases 7 & 8. Cinnabar, or mercuric sulphide, the unique ore of the important metal Mercury. Millerite is the nickel monosulphide, and Greenockite, a rare mineral in bright yellow crystals, consists of the corresponding cadmium sulphide.

and 6.

Case 8.

Case 9.

Case 9.

Sect. iii.

Case 10.

Case 10.

There is also an important series of disulphides wherein Hauerite and Iron-pyrites, which are respectively the persulphide of mangancse and of iron, are cubic, while as Marcasite the latter compound is orthorhombic in crystallisation. These two forms of iron persulphide are frequent and familiar minerals, Iron-pyrites being conspicuous for its sharply defined forms, and Marcasite, or "White Iron-pyrites," for the fantastic groupings in its crystallisation that have obtained for it the various names of Spear pyrites, Cockscomb pyrites, &c.

Molybdenite (Mo S,) and Realgar (As, S2) are severally molybdenum and arsenic disulphides; the former a rhombohedral, the latter an oblique mineral.

Here also is included Laurite, the rare ruthenium sulphide.

Among the trisulphides we find some important compounds of the triad elements crystallising in the orthorhombic system. They are Orpiment, or arsenic trisulphide (As, S), and the two isomorphous trisulphides of Bismuth and Antimony, Bismuthite (Bi, S ̧) nd Antimonite (Sb, S). Of both the last minerals, and in particular of Antimonite, very fine specimens are in this Table Case. Antimonite is an important source of the metal Antimony.

The third section of the division is composed of minerals wherein certain arsenidǝs, &c, of Section i. are combined with sulphides of Section ii., or which may be looked on as the result of a replacement of half the Arsenic of the minerals in the former section, by its equivalent of Sulphur. Of these there is a cubic series, including Cobaltine, or Cobalt-glance, the "Silver White Cobalt" of early mineralogists, a Cobalt Sulphide with part of the Sulphur replaced by Arsenic and part of the Cobalt by Iron {(Co, Fe) (S. As),}. In Gersdorfite or Arsenical Nickel-glance, half the Sulphur is replaced by Arsenic, and in Ullmannite or Antimonial Nickel-glance by Antimony and Arsenic.

In this section, also, the minerals of this chemical type exhibit a dimorphism similar to that of Pyrites and Marcasite among the disulphides of Section ii., and of Rammelsbergite and Chloanthite among the diarsenides of Section i.; for in Mispickel and Glaucodote we

find arsenio-sulphides of Iron and of Cobalt with Iron of the same Div. II. chemical type as Cobalt-glance, but crystallised in the orthorhombic system. Thus the three homotypic series of cubic diarsenides, disulphides, and diarseniosulphides belonging to the three sections of this division might be treated as a single group, while the three corresponding trimetric series may be looked on as another such group.

Besides the three sections already described, this division contains Sect. iv. a fourth, wherein metallic sulphides are so combined with sulphides of Arsenic, Tin, Iron, &c., as to produce a series of sulphur salts; Cases 10, in the constitution of which Sulphur plays the part which Oxygen 11, 12. plays in the ordinary oxygen-salts. This section is a numerous one in point of species, and the following are a few minerals included in it that are especially worthy of note.

In one (and that a somewhat ambiguous) class of these Salts, Iron, either as an iron sesquisulphide (Fe, S) or an iron persulphide (Fe S2), would seem to enter as a constituent of the "acid" ingredient. In this class we meet with two important copper ores, the largely worked Case 10. Chalco-pyrites or Copper-pyrites, and Erubescite or Purple Copper-ore. Of both these minerals, there are crystallised specimens from Cornwall; and massive pieces from Tuscany are seen in the front of Case 7. The rare mineral, Sternbergite, consisting of Iron, Sulphur, and Silver, belongs also to this class; while Linnæite, or "Cobalt-pyrites," (Co, S., CoS,) is a sulphur-compound of Cobalt, exactly analogous to the oxygen-compounds termed the "maguetic oxides" of Iron or Manganese.

Tin-pyrites is a dibasic cuprous sulphostannate, containing Iron and Case 11.

Zinc.

The largest class of the sulphur salts is that consisting of sulpharsenites, sulpho-bismuthites, and sulph-antimonites. Among these Tetrahedrite (Fahlerz or Grey Copper ore), is noticeable as a most Case 11. important ore of Copper. It is a tetra-basic sulph-antimonite of that metal, in which the copper is frequently replaced by small quantities of silver, and is also associated with sulphides of Iron and Zinc. In some of its varieties, as in Tennantite, the Antimony trisulphide is entirely, and in others partially, replaced by an equivalent of Arsenic trisulphide. The argentiferous Tetrahedrite is a valuable ore of Silver. Remarkable specimens of Bournonite, a tri-basic sulph-antimonite of Copper and Lead from the Herod's-foot mine in Cornwall, are here in juxtaposition with those from the Hartz, and from Traver- Case 11. sella. The so-called Red Silvers, a group of isomorphous rhombohedral minerals, are the tri-basic sulphantimonite and sulpharsenite of Silver, Pyrargyrite and Proustite; sometimes in a comparatively isolated Case 12. state, but more frequently blended together in various proportions. Beautiful as well for their forms as for their blood-red colours, that are deeper in tint according as the antimony preponderates over arsenic, they constitute one of the more precious of the ores of Silver. The specimens of Pyrargyrite and Proustite exhibited in Case 12, and in particular those of the latter mineral from Chili, are extremely fine.

E

DIV. II. Case 12.

Div. III.

Sect. i. Cases 13,

14.

Case 13.

Sect. ii. Case 14.

Div. IV. Cases 15, to

60.

Section i.

Among these a large mass of resplendent crystals, of a rich ruby colour by transmitted light, was presented by H. Ludlam, Esq., and is a unique specimen.

Among the rarer minerals, attention may be called to the fine specimens of a variety of Freieslebenite, from Hiendelencina, in Spain; also to Fireblende and Xanthocone, the latter containing a tri-basic sulpharsenate and sulpharsenite of Silver; and to the series. of minerals from the Biunenthal, including very fine crystals of Jordanite.

DIVISION III. COMPOUNDS OF THE HALOGEN ELEMENTS.

With

This next principal division of the Collection is also subdivided into the simpler compounds, and a more complex section of Salts. Among the former will rank Calomel, Salammoniac, Common Salt (Sodium chloride), and Sylvine, the corresponding potassium chloride, the two latter being crystallised in large cubes and cubo-octahedra. these are arranged the chloride, iodide and bromide of Silver, and the mixtures of these inter se which are kept secluded from the light. The crystal forms and colour suite of Fluor spar exhibited in Case 14, form a series as remarkable for beauty as any in the Collection.

The Salts in this division are represented by certain double fluorides, of which the most important is the Greenland mineral Cryolite (sodium aluminium fluoride), represented by some excellent specimens in its crystallised form.

DIVISION IV. COMPOUNDS OF OXYGEN.

The remaining division consists of Minerals of which Oxygen is a constituent ingredient, a class necessarily large on a planet with an atmosphere consisting in considerable proportion of this chemically energetic element. The rocks which constitute the earth's crust, are aggregates of minerals falling under this chemical division. Here, as in the previous divisions, we distinguish the more simple kinds of combination from the more complex; and though such a distinction as is expressed by a section of oxides and a section of salts is a difficult one to define with logical precision, it yet serves the object sought in a system of classification, by bringing together compounds that most closely resemble each other, the different classes falling into a natural sequence, nearly in the order of the simplicity of their chemical formulæ. The first section of this chemical division, the Oxides, will be found arranged in Cases 15 to 26, those containing the greater proportion of oxygen following after those that contain fewer. Commencing with basic types of oxides, we pass through certain comparatively neutral oxides (among which we must look for those members of the section which possess the most equivocal claim to a place in this section); and we then come to the higher oxides which act the part of acids in combining with bases.

The oxides include several very important minerals. First in order

among them is Cuprite, the red oxide of Copper, cuprous oxide. It Div. IV. occurs in ruby-coloured and transparent crystals of the cubic system. Case 15. These are seen in the first half of Case 15, and with them are the "Tile ore," from the Urals, and the bright-red capillary deposits of Chalcotrichite. The cupric oxide, as Melaconite and Tenorite, succeeds to the crystalline oxides of Magnesium (Periclase), and of Zinc (red oxide of Zinc, or Zincite), in the other half of this Case. These are followed, first by the hydrated monoxides, including Brucite, the magnesium hydrate, which presents delicate hexagonal transparent crystals; in succession to which are minerals in which oxides of this type are associated with compounds belonging to preceding Divisions of the Collection. The lead-oxychlorides, Matlockite and Mendipite, are arranged here with Atacamite, a cupric chlorhydrate, and of Percylite, a beautiful mineral, of which one specimen, of uncertain locality, is associated with Gold. It is a hydrated combination of the oxychlorides of Lead and Copper.

The next class in the section of oxides is composed of minerals of a chemical type, similar to that of the magnetic oxide of Iron (the Case 16. ferro-ferric oxide), which may in fact be viewed as a combination of (ii.) ferrous oxide with ferric oxide, and thus, while possessing the formula and a place in the section of the oxides, has claims to be recognised as a salt. For the group of cubic-formed minerals to which Magnetite more especially belongs, the "Spinel Group," includes Franklinite and Chromite (Chromic-iron), which latter mineral is the source of the chrome yellow and of some other colouring matters employed in the arts. The Spinels, properly so called, also belong to it. These are Case 16 (i.) aluminates of Magnesium, of Zinc, Iron, or Manganese; ferric oxide occasionally playing the part of alumina. The deep-red "Spinel Ruby" and the pale rose-tinted "Balas Ruby " are beautiful gems cut from specimens of this Mineral, of which a good assortment of crystals is exhibited. Pleonast, Gahnite, Dysluite, are opaque varieties of Spinel. To this class also may be referred the Chrysoberyl, a combination of glucina and alumina (glucinum aluminate), belonging to the same type. It is orthorhombic in crystallisation, and as a gem, known by the name of "oriental chrysolite," it presents itself as a Case 16. beautiful greenish yellow stone, equal in lustre and almost in hard- (ii.) ness to the Sapphire. The variety Cymophane is so named from a cloudy appearance that presents itself in two of the faces of the crystal, and is retained even when the transparent stone is cut and polished. Cut en cabochon, the less transparent specimens furnish one of the kinds of stone to which the jewellers give the name of Cat's-eye. Of the dark green variety from the emerald mines of the Ural, termed Alexandrite, very fine specimens are seen in this Case. It is amethyst-coloured by artificial light.

The next class among the oxides is that of the sesquioxides. Case 17. The pure oxide of Aluminium is seen in colourless crystals of Corundum, consisting for the most part of hexagonal pyramids and prisms. With minute traces of colouring ingredients, these crystals assume rich hues, and when transparent become gems