Chalcopyrite

“ Argentite, the simple sulphide of silver, is the chief source from which silver is obtained. It looks like galena, and has the same hardness, streak and specific gravity, but can be distinguished by the galena having a very perfect cubic cleavage while the argentite has no cleavage. Argentite is easily cut with a knife (sectile) . It is usually found in irregular masses, but sometimes in cubes which make very choice cabinet specimens; and is associated with such other minerals as galena, sphalerite, chalcopyrite, pyrite, fluorite, quartz, and calcite. ”

“ It is perhaps superfluous to say that nodules of chalcedony, often hollow and containing crystallized quartz, are occasionally found in the trap rocks of Sky, since they are of such common occurrence in this substance. The cavities are sometimes, in addition, sprinkled with crystals of stilbite, of analcime, and of chabasite.
Of those mineral substances which are the least frequent in trap rocks, steatite occurs in considerable quantity; it is tender, and always of a greenish dirty hue. It is sometimes found in very small nodules ”

“ The chalk formations or “cretaceous group of beds” include strata of various mineral substances; but the white chalk which forms the cliffs of Dover and the adjoining coasts, and the downs and chalk quarries of the South of England, is the chief and most characteristic formation. Chalk, immense as are the masses in which it has been deposited, owes its origin to living actions; every particle of it once circulated in the blood or vital juices of certain species of animals, or of a few plants, that lived in the seas of the secondary period of geological time. ”

“ Calcite.--This mineral occurs in great abundance in and about the tunnel, and from all the shafts. There are two forms occurring there, the most abundant of which is the rhombohedral, after Fig. 3. It can generally be obtained, however, in excellent crystals, which, although perfect in form, are opaque, but often large and beautiful. It is always packed with a thousand or its multiple of other crystals into veins of a few inches thick; and crystals are obtained by carefully breaking with edge of the cold chisel these masses down to the fundamental form shown. ”

“ Further, equivalent amounts of the different chemical elements represented by R” are mutually replaceable, and two or more of these elements may be present together in the same crystal, which is then spoken of as a “mixed crystal” or isomorphous mixture.
In another isomorphous series of carbonates with the same general formula R′′CO3, where R′′ represents calcium, strontium, barium, lead or zinc, the crystals are orthorhombic in form, and are thus dimorphous with those of the previous group (e.g. calcite and aragonite, the other members being only represented by isomorphous replacements) . ”

“ Fig. 1. [1] This figure is given for the purpose of explaining the mode in which the fibrous disposition of chlorite is effected. The crystallized arrangement which is here so visible is generally observed in those chlorite fibres which occur in transparent quartz. I I have never observed it in chalcedony, yet there is little doubt that a similar disposition is equally the cause of the fibrous appearance so common in the specimens which have been figured in the former plates, the chief differences consisting in the smaller size and less perfect crystallization of the chlorite scales. ”

“ By modern mineralogists the name chalcedony is restricted to those kinds of silica which occur not in distinct crystals like ordinary quartz, but in concretionary, mammillated or stalactitic forms, which break with a fine splintery fracture, and display a delicate fibrous structure. Chalcedony may be regarded as a micro-crystalline form of quartz. It is rather softer and less dense than crystallized quartz, its hardness being about 6.5 and its specific gravity 2.6, the difference being probably due to the presence of a small amount of opaline silica between the fibres. ”

“ Fairly widespread in small amounts, and in commercial quantities in only a few localities, usually in veins in granite or metamorphic rocks near granite, as at Cornwall, England, also in the form of rounded masses in gravel deposition as in the Malay region.
Chalcocite. Crystallizes in the orthorhombic system, usually in tabular form, but crystals not common. A black sulphide of copper with metallic luster. Hardness, nearly 3; specific gravity, nearly 6. No cleavage. Chalcocite occurs in vein deposits as one of the important copper ores, especially at Butte, Montana. ”

“ PYROMORPHITE, a mineral species composed of lead chlorophosphate (PbCl) Pb4 (PO4) 3, sometimes occurring in sufficient abundance to be mined as an ore of lead.
Crystals are common, and have the form of a hexagonal prism terminated by the basal planes, sometimes combined with narrow faces of a hexagonal pyramid. Crystals with a barrel-like curvature are not uncommon. Globular and reniform masses are also found. As proved by the etched figures on the faces, crystals possess the same parallel-faced hemihedrism as apatite, with which mineral pyromorphite and also mimetite are isomorphous. ”

“ But the slice of chalk presents a totally different appearance when placed under the microscope. The general mass of it is made up of very minute granules; but, imbedded in this matrix, are innumerable bodies, some smaller and some larger, but, on a rough average, not more than a hundredth of an inch in diameter, having a well-defined shape and structure. A cubic inch of some specimens of chalk may contain hundreds of thousands of these bodies, compacted together with incalculable millions of the granules. ”

“ Chalcedony, kal-sed′ō-ni, or kal′-, n. a beautiful mineral of the quartz family, consisting of quartz with some admixture of opal—it is generally translucent, has a somewhat waxy lustre, and is in colour generally white or bluish-white.—adj. Chalcedon′ic.—n. Chalced′onyx, an agate formed of a white opaque chalcedony alternating with a grayish translucent chalcedony. [Prob. from Chalcedon, in Asia Minor.] ”

“ A white fossil substance, by some reckoned a stone, but of a friable kind, which cannot, therefore, be polished as marble; by others, more properly ranked among the earths. It is of two sorts, one a hard dry chalk, used for making lime; the other a soft, unctuous kind, used in manuring land, &c. Chalk always contains quantities of flint-stone, and the fossil remains of shells, coral, animal bones, marine plants, &c.; from which circumstance there can be no doubt that chalk is the deposited mud of a former ocean. The chemical name of chalk is carbonate of lime. ”

“ And, for reasons which you will hardly understand, men are beginning now to believe that the chalk has never ceased to be made, somewhere or other, for many thousand years, ever since the Winchester Downs were at the bottom of the sea: and that “the Globigerina-mud is not merely a chalk formation, but a continuation of the chalk formation, so that we may be said to be still living in the age of Chalk.” ”

“ Similarly contorted fibres occurring in chalcedony do not exhibit the crystallized structure, but appear to consist of very minute or of invisible particles, or even of a mere colour diffused in that particular form. At times the coloured fibre contains grains of chlorite attached to its sides or interspersed through its course, thus emulating the imbedded seeds or jointed appearance of real confervæ, and I have reason to think often mistaken for them. ”

“ But what shall we say when the investigations of the microscope have lately revealed to us that these mountains of chalk, instead of being formed of mere inert matter, are, on the contrary, mighty congeries of decayed animal life,—the white apparent particles, of which the chalk masses are composed, being each grain a well-defined organized being, in form still so perfect, their shells so entire, and all their characteristics so discoverable, as to cause no doubt to naturalists as to the species in the animal economy to which they belonged. ”

“ Thus our European Chalk formation can be recognised in many distant parts of the world, under the most different climates, where not a fragment of the mineral chalk itself can be found; namely, in North America, in equatorial South America, in Tierra del Fuego, at the Cape of Good Hope, and in the peninsula of India. For at these distant points, the organic remains in certain beds present an unmistakeable degree of resemblance to those of the Chalk. It is not that the same species are met with ”

“ The perfect state of the surfaces of the chalk fossils proves also that this deposition proceeded from the surrounding fluid, and that it was not derived from the immediate action of any chemical agent, on the shells and other calcareous coverings of the animals living at the bottom of the sea. In the fossil animal bodies found in chalk, not the least diminution of the sharpness of their ridges or points is observable, nor is the least dulness of the delicate lines and embossments of the crusts, or of the spines of the echini, to be detected. ”

“ CALCITE, a mineral consisting of naturally occurring calcium carbonate, CaCO3, crystallizing in the rhombohedral system. With the exception of quartz, it is the most widely distributed of minerals, whilst in the beautiful development and extraordinary variety of form of its crystals it is surpassed by none. In the massive condition it occurs as large rock-masses (marble, limestone, chalk) which are often of organic origin, being formed of the remains of molluscs, corals, crinoids, &c., the hard parts of which consist largely of calcite. ”

“ In these cavities we recognize an exact counterpart to those which are so numerous on the furrowed surface of our own white chalk. Advancing from these quarries along a road made of the white limestone, which reflects as glaring a light in the sun, as do our roads composed of chalk, we reach, at [p.189] length, in the neighbourhood of Aurillac, hills of limestone and calcareous marl, in horizontal strata, separated in some places by regular layers of flint in nodules, the coating of each nodule being of an opaque white colour, like the exterior of the flinty nodules of our chalk. ”

“ In these specimens (brought from Egypt) distinct grains of green matter may be observed independent of the general green stain which pervades the stone; and this probability is rendered still stronger from the colour and appearance which is occasionally assumed by the more transparent flinty matter associated with the chalcedony, the latter acquiring from the chlorite the aspect of heliotrope, while the more transparent parts put on the semblance of plasma. But of a substance so rare it is necessary to speak with hesitation. ”

“ In some cases perfect crystals of chabasite are lightly sprinkled over the surface of crystals of stilbite, adhering so slightly as to fall off on the slightest concussion: in other cases crystals of this mineral, as well as of the analcime, are confusedly mixed with rhomboids of carbonate of lime, hereafter to be described. ”

“ In chemical composition, true chalk is calcium carbonate, but of a fossil character, for if chalk dust be examined under a high-power microscope, it will be seen to consist of the shells of minute animals, and is therefore to be regarded as fossil. The organic matter of the animals has long disappeared, leaving the inorganic material, a very pure calcium carbonate, behind. ”

“ But the internal structure retains traces of all its tubes and fibres, most delicately preserved in a reddish chalcedony. The introduction of this chalcedony appears to have been subsequent to the first incasing of the body by the coarse siliceous crust, and contemporaneous with the gradual decay of the animal matter inclosed, the particles of chalcedony being successively introduced into the space vacated by the animal particles as they successively perished, till the result was an entire substitution of chalcedony bearing the form of the organization of the animal. ”

“ One sees at first crystal skeletons, then gradually the crystals developing into perfection. Neither the chemist with all his delicate tests, nor the physician armed with his accurate instruments can decipher the feeblest trace of heterogeneity; the child grown has become a man; the mineral fully developed has reached also its age of virility.
Minerals may be hindered in their development, may become irregular, imperfect, deformed; upon certain of their angles new facets may appear, in other parts facets may slowly become obliterated. ”

“ In many others no mechanical texture or disposition can be discovered in the stone, but the whole appears one semitransparent mass of chalcedony. These are the specimens in which the confervæ preserve that freedom of arrangement and that perfection both of colour and structure which seem to imply that they had been so suddenly involved in a mass of siliceous matter as to have been preserved from all future changes. Many other specimens have that mixed aspect of jasper and chalcedony to which among other varieties of ornamental stones the lax term of agate has been, applied. ”

“ As a pigment, chalk possesses many valuable properties. The organic structure of chalk gives it high covering power as a wash, a thin layer applied to a surface sufficing to mask the colour of the underlying ground completely. The lime in chalk being combined with carbonic acid, its basic properties are so extensively weakened that chalk can be mixed with even the most delicate colours without fear of their shade being affected. A coating of pure chalk paint on any surface will never change colour in the air ”

“ Phosphate of chalk is not in reality (as I wished to prove in another work) a plastic matter suitable for forming bones, for the bones of infants are three times more solid than those of old men, which contain three times as much of it. The quantity of phosphate of chalk necessary to the constitution of animals is in proportion to the temperature of those animals, and often in the inverse ratio of the weight of their bones, for vegetables, although they have no bones, require phosphate of chalk. ”