2. Cohesion of particles; distinguished into solid, friable, and fluid.

In solid minerals are to be regarded the external shape, lustre, and surface. When broken, the lustre of the fracture, the fracture itself; and the shape of the fragments are to be noticed. In distinct concretions regard must be paid to the shape of the concretions, their surface, their lustre, transparency, streak and soiling. All these may be ascertained by the eye. By the touch we may discover the hardness of minerals, their tenacity, frangibility, flexibility, their unctuosity, coldness, weight, and adhesion to the tongue. By the ear we distinguish their sound; and by the smell and taste the qualities which these two senses indicate.

In friable minerals, external shape, lustre, aspect of particles, soiling, and degree of friability, are to be attended to.

In fluid minerals the lustre, transparency, and fluidity, are principal objects to be regarded.

The specific external characters of minerals are founded on the distinctions and varieties of the two great generic divisions. And first, of colours, the

names of which are derived from certain bodies in which they most generally occur, either in a natural or artificial state, or from different mixtures and compositions of both.

I. COLOUR.

1. White. This may be snow-white, reddish-white, yellowish-white, silver-white, greyish-white, greenishwhite, milk-white, or tin-white.

2. Grey. Lead-grey, bluish-grey, pearl-grey, reddish-grey, smoke-grey, greenish-grey, yellowishgrey, steel-grey, and ash-grey.

3. Black. Greyish-black, brownish-black, dark black, iron-black, greenish-black, and bluish-black.

4. Blue. Indigo-blue, Prussian-blue, lavenderblue, smalt-blue, sky-blue.

5. Green. Verdegris-green, celaden-green, mountain-green, emerald-green, leek-green, apple-green, grass-green, pistachio-green, asparagusgreen, olive-green, blackish-green, canary-green.

6. Yellow. Sulphur-yellow, lemon-yellow, goldyellow, bell-metal-yellow, straw-yellow, wine-yellow, Isabella-yellow, ochre-yellow, orange-yellow, honeyyellow wax-yellow, brass-yellow.

7. Red. Morning-red, hyacinth-red, brick-red, scarlet-red, copper-red, blood-red, carmine-red, cochineal-red, crimson-red, columbine-red, flesh-red, rose-red, peach. blossom-red, cherry-red, brownishred.

8. Brown. Reddish-brown, clove-brown, hairbrown, yellowish-brown, tombac-brown, wood-brown, liver-brown, blackish-brown.

Besides these distinctions, colours may be clear, dark, light, or pale; they may have a tarnished appearance, a play, a changeability, an iridescence, an opalescence, a permanent alteration, and a delineation of figure or pattern, such as dotted, spot

II. COHESION OF PARTICLES.

Minerals are divided into, 1. Solid, or such as have their parts coherent, and not easily moveable; 2. Friable, or that state of aggregation in which the particles may be overcome by simple pressure of the finger; and 3. Fluid, or such as consist of particles which alter their place in regard to each other by their own weight.

1. Solid Minerals.

External aspect has three things to be regarded,

The shape; 2. The surface; and 3. The lustre. The external shape again may be common, particular, regular, or extraneous; and hence arise the specific differences.

1. The common external shape may be massive; disseminated coarsely, minutely, or finely; in angu lar pieces, sharp-cornered or blunt-cornered; in grains, large, coarse, small, fine, angular, flat, round; in plates, thick or thin; in membranes or flakes, thick, thin, or very thin.

The particular external shape may be longish, as dentiform, filiform, capillary, reticulatic, dendritic, coralliform, stalactitic, cylindrical, tubiform, claviform, or fruticose; roundish, as globular, spherical, ovoidal, spheroidal, amygdaloidal, botryoidal, reniform, tuberose, or fused-like; flat, as specular, or in leaves; cavernous, as cellular in various forms, with impressions, perforated, corroded, amorphous, or vesicular; entangled, as ramose, &c.

In the regular external shape or crystallization are to be regarded its genuineness, according to which it may be either true or suppositious; its shape, made up of planes, edges, angles, in which are to be observed the fundamental figure and its parts, the kind of fundamental figure, the varieties of each kind of fundamental figure, with their accidents and distinctions, and the alterations which the fundamental figure undergoes by truncation, by bevelment, by acumination, or by a division of the planes. There are a variety of figures under each of these subdivisions.

It must be remarked also, that the external shape may be extraneous, or derived from the animal and vegetable kingdoms, as in fossils and petrifi

cations.

2. The external surface contains several varieties of distinctions. It may be uneven, granulated, rough, smooth, or streaked in various ways and directions.

3. The external lustre is the third generic external character, and is of much importance to be attended to. In this we have to consider the intensity of the lustre, whether it is splendent, shining, glistening, glimmering, or dull, next the sort of lustre, whether metallic or common. The latter is distinguished into semimetallic, adamantine, pearly, resinous, and vitreous.

Aspect of the Fracture of solid Minerals.

After the external aspect, the fracture forms no inconsiderable character in minerals. Its lustre may be determined as in the external lustre; but the fracture itself admits of great varieties. It may be compact splintery, coarsely splintery, finely splintery, oven, conchoidal, uneven, earthy, hackly. If the fracture is fibrous, we are to consider the thickness of the fibres, if coarse or delicate; the direction of the fibres, if straight or

curved; and the position of the fibres, if parallel or diverging.

In the radiated fracture we are to regard the breadth of the rays, their direction, their position, their passage or cleavage. In the foliated fracture, the size of the folia, their degree of perfection, their direction, position, aspect of their surface, passage or cleavage, and the number of cleavages, are to be noted.

The shape of the fragments may also be very varous-regular, as cubic, rhomboidal, trapezoidal, &c.

or irregular, as cuneiform, splintery, tabular, indeterminately angular.

Aspect of the distinct Concretions.

The shape of the distinct concretions forms very prominent external characters. They may be granuiar, different in shape, or in magnitude; they may be lamellar, distinct, concretious, differing in the direction of the lamellæ, in the thickness, with regard to shape, and in the position.

The surface of the distinct concretions may be smooth, rough, streaked, or uneven; as for their lastre, it may be determined in the same manner as the external lustre.

General Aspect as to Transparency. Minerals, as is well known, have different degrees of transparency, which may be considered among their external characters. They may be transparent, semitransparent, translucent, translucent at the edges, or орацие.

The Streak.

The colour of this external character may be either similar or different. It is presented to us when a mineral is scraped with the point of a knife; and is similar when the powder that is formed is of the same colour with the mineral, as in chalk: or dissimilar or diferent, as in cinnabar, orpiment, &c.

The Soiling or Colouring

Is ascertained by taking any mineral substance betreen the fingers, or drawing it across some other Lody. It may soil strongly, as in chalk; slightly, as in molybdena; or not at all which is a quality belonging to most of the solid minerals. All the preceding external characters are recognized by the eye.

External Characters from the Touch.

These are eight in number, and are not destitute of utility to the mineralogical student. 1. Hardness; 2. Tenacity; 3. Frangibility; 4. Flexibility; 5. Adbesion to the tongue; 6. Unctuosity; 7. Coldness; 8. Weight.

Hardness may be tried by a capacity to resist the file, yielding a little to it, by being semi-hard, soft, or very soft. Tenacity has different degrees, in substances being brittle, sectile or mild, or ductile. The frangibility consists in minerals being very difficultly frangible, difficultly frangible, easily frangible, or very easily frangible. The flexibility is proved by being simply flexible, elasticly flexible, commonly flexible, or inflexible. The adhesion to the tongue may be strongly adhesive, pretty strongly, weakly, very weakly, or not at all. Unctuosity may be meager, rather greasy, Coldness is subdivided into greasy, or very greasy. cold, pretty cold, rather cold. Weight may be distinguished into swimming or supernatant, light, rather light, heavy, very heavy. The three last divisions from the touch are in the Weruerian system regarded

as anomalous; but they seem properly to be classed under this head.

External Characters from the Sound or Hearing.

The different kinds of sound which occur in the mineral kingdom are, 1. A ringing sound, as in native arsenic and thin splinters of horn-stone; 2. A grating sound, as in fresh-burnt clay; 3. A creaking sound, as that of natural amalgam.

2. Friable Minerals.

The external characters drawn from minerals of this class are derived, first, from the external shape, which may be massive, disseminated, thinly coating, spumous, or dendritic: secondly, from the lustre, regarded under its intensity, whether glimmering or dull, and its sort, whether common glimmering or metallic glimmering: thirdly, from the aspect of the particles, as being dusty or scaly fourthly, from soiling or colouring, as strongly or lightly: and lastly, from the friability, which may be loose or cohering.

These may be spontaneously emitted and described, as bituminous, faintly sulphureous, or faintly bitter; or they may be produced by breathing on, and yield a clay-like smell: or they may be excited by friction, and smell urinous, sulphureous, garlic-like, or empyreumatic.

External Character from the Taste.

This character prevails chiefly in the saline class, and it contains the following varieties: a sweetish taste, sweetish astringent, styptic, saltly bitter, saltly cooling, alkaline, or urinous.

Having now given a synoptical view of the external characters of minerals, we shall proceed to their classification, and in this we shall chiefly follow the names and arrangement of professor Jameson.

CLASS I.
EARTHY FOSSILS.
First Genus. DIAMOND.

Diamond.

This precious stone has great variety of shades, exhibiting a beautiful play of colours. It occurs in indeterminately angular and completely spherical grains, which present planes of crystallization, or are actually crystallized. Its fundamental crystal is the It is octaedron, which passes into various forms. hard in the highest degree, brittle, not very difficultly frangible, and has a specific gravity of 3.600.

The diamond has, by modern experiments, been proved to be nearly pure carbon, and begins to burn at 14 or 15° of Wedgewood. See 'late 107. Mineralogy, figs. 1. and 2.

Second Genus. ZIRCON.
First Species. Zircon.

The prevailing colour is grey, but it occurs like

wise green, blue, red, yellow, and brown, with various intermediate tints.

It is found most commonly in roundish angular pieces, with rounded angles and edges. When crystallized, the figure is generally a rectangular foursided prism; somewhat flatly acuminated by four planes, set on lateral planes; but of this figure there are several varieties. The crystals are almost always very small, have a smooth surface, bordering on strongly splendent. Internally, the lustre is strongly splendent, passing into adamantine. Fig. 3.

Zircon is hard in a very high degree, brittle, frangible without great difficulty. Specific gravity 4.700. It forms a colourless transparent mass with borax, but is infusible by the blow-pipe without addition. Found in the island of Ceylon, where it was first discovered, and lately in Norway, imbedded in a rock composed of hornblend and felspar.

Frequently cut as a precious stone, and used as an inferior kind of diamond, of which it was once considered as a variety. Its play of colours very considerable.

Second Species. Hyacinth.

The chief colour is red, passing to reddish-brown, and to orange-yellow. The figure a rectangular four-sided prism, flatly acuminated by four planes, which are set in the lateral edges. Of this figure,

however, several varieties occur.

The crystals are generally small, and always imbedded. The lateral planes smooth, and externally shining. Internally it is splendent and glassy, inclining somewhat to resinous.

The hyacinth is transparent, very hard, frangible without particular difficulty, feels a little greasy when cut, and has a specific gravity of about 4.000.

Is fusible with borax. Exposed to the blow-pipe it loses its colour, but not its transparency.

Occurs in rocks of the newest floetz trap formation, and sometimes in sand. Is a native of Ceylon, the country of gems; of Spain, of Portugal, France, Italy, Saxony, and probably Scotland.

It takes a fine polish, and when the colours are good, it is highly valued. A third species, called cinnamon stone, has lately been discovered at Columbo, in Ceylon.

Third Genus. FLINT.

First Species. Chrysoberyl.

The prevailing or general colour is asparagusgreen, passing into a variety of allied shades. It exhibits a milk-white light; occurs in roundish and angular grains, which sometimes approach in shape to the cube. It is seldom crystallized; but when in this state it commonly presents a longish six-sided table, having truncated lateral edges, and longitudinally-streaked lateral planes. The crystals are small, externally shining, and internally splendent. Fig. 4.

It is hard, brittle, not very easily frangible, with a specific gravity of 3.600. Without addition it is

infusible.

The chrysoberyl is found in Brazil, and in the sand of Ceylon. It is sometimes set in rings with a yellow foil, but is rarely in the possession of our jewellers.

Second Species. Chrysolite.

The chief colour is pistachio-green, of all degrees of intensity. It occurs in original angular sharpedged pieces, with a rough, scaly, splintery surface, and when crystallized exhibits a broad rectangular

four-sided prism, with its lateral edges sometimes truncated, sometimes bevelled, and acuminated by six planes. Fig. 5.

The external surface of the crystals is splendent, internally splendent, and vitreous.

Third Species. Olivine.

The colour is generally asparagus-green, of various degrees of intensity. It is found imbedded also in roundish pieces and grains; and when crystallized, which is rare, in rectangular four-sided prisms.

Internally, it is shining, varying between glistening and splendent. It is semitransparent, very easily frangible; in a low degree hard, and not particularly heavy. It is nearly infusible without addition. Occurs imbedded in basalt; is frequently found in Bohemia, and also in Hungary, Austria, France, England, Ireland, Scotland, Sweden, Iceland, and Norway. Pieces as large as a man's head have been found in some parts of Germany.

Fourth Species. Augite.

chiefly in indeterminate angular pieces and roundish The general colour is blackish-green. It occurs broad rectangular six-sided prisms. The crystals are grains. Occasionally it is crystallized, and presents mostly small. Internally the lustre is shining, approaching sometimes to splendent.

The augite is only translucent, and but faintly transparent. It is hard, not very easily frangible, and not particularly heavy.

with olivine, in Bobemia, Hungary; at Arthur's-seat, It is found in basalt, either singly or accompanied near Edinburgh; in some of the Hebrides, and in darker colours, the form of its crystallization, and its Norway. From olivine it is distinguished by its greater hardness.

Fifth Species. Vesuviane.

Its principal colour is dark olive-green, passing into other allied shades. It occurs massive, and often crystallized in rectangular four-sided prisms. The crystals are mostly short, and placed on one another. Externally their surface alternates between glistening and splendent. Internally they are glistening, with a lustre between vitreous and resinous.

The vesuviane is translucent, hard in a moderate degree, and approaching to heavy. Before the blowpipe it melts without addition.

It is found among the exuviæ of Vesuvius, from whence it derives its name, in Siberia and Kamtschatka. At Naples, it is cut into ring-stones, and sold under various names.

Sixth Specics. Leuzite.

Seventh Species. Melanite.

The general colour is velvet-black. It occurs crystallized in a six-sided prism. The crystals are middle-sized or small. Externally they are smooth and shining, approaching to splendent; internally shining, inclining to glistening.

The melanite is opake, hard, pretty easily frangible, and not very heavy. It occurs imbedded in rocks of the newest floetz trap formation, and hitherto has been found only at Frescati and St. Albano, near Rome.

Eighth Specics. Garnet.

This is divided into two sub-species, the precious garnet and the common garnet. See GARNET, and tig. 6.

Ninth Specics. Pyrope.

The colour is dark blood-red. It occurs in small and middle-sized roundish and angular grains; but never crystallized. Its lustre is splendent and vitreous. It is completely transparent, hard so as to scratch quartz, and not particularly heavy.

The pyrope is found imbedded in serpentine in Saxony and Bohemia. In Fifeshire, Scotland, it is found in the sand on the sea shore. It is employed in various kinds of jewellery, and is generally set in a good foil.

Tenth Species. Grenatite.

The colour is a dark reddish-brown. It is always crystallized in broad six-sided prisms. The crystals are small and middle-sized, internally glistening, with a lustre between vitreous and resinous.

The grenatite varies from opake to translucent, is hard, brittle, easily frangible, and not particularly heavy.

It is found imbedded in mica slate, in St. Gothard, Switzerland; and is also met with in Britanny and in Spain.

Eleventh Species. Spinelle.

The predominant colour is red, which passes on into blue, green, yellow, and brown. It occurs in grains, and likewise crystallized in octaedrons with several variations. The crystals are very rarely middle-sized. Externally and internally the lustre is splendent and vitreous.

The spinelle alternates from transparent to vitreous: it is hard in a pretty high degree, and approaches to heavy. It is fusible with borax; occurs in rocks belonging to the newest floetz trap formation; and is found in Pegu and Ceylon. It is used as a precious stone, and considerably valued, though possessing neither the hardness nor the fire of the oriental ruby.

Twelfth Species. Sapphire.

The principal colour Berlin blue; but it is found also red, with all the intermediate shades between these two colours. It occurs in small rolled pieces, and crystallized in double three-sided pyramids, of which there are several varieties in figure.

The crystals are small and middle-sized. Intermally the lustre is splendent and vitreous. It is more or less transparent in different specimens. Some varieties, when cut, exhibit a star of six rays. Fig. 7. The sapphire is hard in the highest degree, but yields to the diamond; it is easily frangible, and rather beavy, having a specific gravity of about 4.000.

It is infusible without addition; occurs in rocks of

the newest floetz trap formation, and is supposed to be an inmate of granite, syenite, and other primitive rocks.

in Pegu and Ceylon. It is also a native of Portugal, This precious stone is found in the utmost beauty of France, and of Bohemia. Next to the diamond, it kind of jewellery. is the most valuable of gems, and is used in the finest

It should be observed, that the violet-coloured sap

phire is the oriental amethyst; that the yellow is the oriental chrysolite and topaz; and that the green is the oriental emerald.

Thirteenth Specics. Corundum.

The principal colour is a greenish-white, of various degrees of intensity. It occurs massive, disseminated, in rolled pieces, and crystallized. The crystallizations resemble those of the sapphire, and the crystals are middle-sized and imbedded.

The corundum is duplicating translucent, hard in a high degree, pretty easily frangible, and approaches to heavy. It is supposed to occur imbedded in granite, syenite, or green-stone, and is found in the Carnatic and on the coast of Malabar. See CORUNDUM.

Fourteenth Species. Diamond Spar.

The colour is a dark hair-brown. It occurs massive, disseminated, in rolled pieces, and crystallized in six-sided prisms, or very acute six-sided pyramids. Internally, its lustre is splendent, approaching in a slight degree to adamantine. It may be cut so as to present an opalescent star of six rays, of a peculiar pearly light.

It is translucent on the edges, hard in a high degree, easily frangible, and not particularly heavy.

The diamond spar probably occurs in granite. It has hitherto been found only in China. Both this stone and corundum are employed in cutting and polishing hard minerals, and they seem to be nearly allied to each other.

Fifteenth Species. Emery.

Emery is hard in the highest degree, not very easily frangible, and is heavy. It occurs in beds of tale and steatite, and is frequently accompanied with calespar and blende. It is found in Saxony, in the islands of the Archipelago, in Spain, Normandy, and is said also to be a native of the isles of Guernsey and Jersey. It is of great use in cutting and polishing hard bodies.

Sixteenth Species. Topaz

The chief colour is a wine-yellow, of all degrees of intensity. It is found massive, disseminated, and sometimes rolled, but most commonly crystallized in oblique eight-sided or four-sided prisms, which exhibit several varieties. The crystals are small and middlesized, externally splendent; internally splendent, and shining; lustre vitreous.

The topaz alternates from translucent to transparent, and is duplicating transparent. It is hard in a high degree, easily frangible, and is not particularly heavy. It is fusible with borax; and some kinds in a gentle heat turn white, and are sometimes sold for diamonds.

It is commonly found in veins that traverse primitive rocks in Brazil, Siberia, in Pegu, and Ceylon; in Bohemia, Saxony, and in Cornwall. Exhibiting various forms and tints, it has often been confounded with other precious stones. It is much used in seals and rings.