Mineralogy

“ Without doubt the multitudinous facts of mineralogy assembled during the past century by the painstaking investigation of a large number of scientists are destined to play a large part in the solution of this problem. Further, it does not seem too bold a prophecy to suggest, that the time will come when it will be possible to assemble all these unorganized facts that we know about minerals into a harmonious whole and that we shall be then able to formulate the underlying and fundamental principles upon which they all depend. ”

“ To the beginner the usual textbook of mineralogy is difficult to read intelligently, for the reason that for each mineral species it sets before him a catalogue of each physical property in its turn, with little indication of those data which in the individual case have special diagnostic value. None the less, however, the student is advised to consider the several properties of each mineral in a definite order, and the following may serve as well as any: crystal or other form, cleavage, fracture, luster, color, streak, transparency, tenacity, hardness, magnetism, and specific gravity. ”

“ It is a matter of regret, that mineral species are so often brought out, especially in this country, without sufficient investigation and full description. It is not meeting the just demands of the science of mineralogy to say that a mineral has probably certain constituents, or to state the composition in a general way without a complete and detailed analysis, especially when there are no crystallographic characters to afford the species a good foundation. ”

“ It is thus that I have been told by men of great mineral knowledge, men who must have had the best education upon that subject of mineralogy, and who have the superintendance of great mineral concerns in Germany, that they had actually seen nature at work in that operation of forming rock-crystal;—they saw what I have now described ”

“ With slight exceptions minerals are the materials which make up the known part of the earth. In a very real sense, then, mineralogy is the most fundamental of the various branches of the great science of geology because the events of earth history, as interpreted by the geologist, are recorded in the mineral matter (including most rocks) of the earth. When we examine the rocky material or mineral matter of the earth in any region we find that it consists of various kinds of substances each of which may be recognized by certain characteristics. ”

“ Synthesis of Minerals.—The production of minerals by artificial means is a branch of chemical mineralogy which has been pursued with considerable success, especially by French chemists. Most minerals have been obtained artificially in a crystallized condition, and many related compounds, not as yet found in nature, have also been prepared. Crystals of artificially prepared minerals, though usually quite small in size, possess all the essential characters of natural crystals, differing from these only in origin. ”

“ All parts of minerals are alike. There are simple minerals and mixed. The former are the true minerals, and are generally considered under the heading Mineralogy. The others constitute a branch of Geology, as they form aggregate masses, and as such compose a large portion of the earth. We must learn to distinguish minerals and crystals as inorganic forms of nature. In the animal and vegetable kingdoms we have forms which are possessed of organs of sight, smell, taste, and certain structures indispensable to their existence and development. But in minerals we have no such attributes. ”

“ We commonly look upon it in the light of an useful handmaiden, whose chief function is to serve the other branches, and we are inclined to forget that, in reality, mineralogy was the first to be recognized and, with considerable truth, might be claimed as the mother of all the others. ”

“ In fact there is no mineral hitherto known which we might not assume as the commencement of a series, and thence proceed to establish by insensible shades a circuit comprehending the whole of those which have been already determined, and the more extensive our acquaintance with mineralogy the more will the truth of the observation become apparent, in consequence of the more numerous varieties and shades of difference which will be discovered. ”

“ More than 800 well-established mineral species have been described since the year 1800, of which approximately 150 have been from American sources. More than two-thirds of the articles describing these new American minerals have first appeared in the pages of the Journal. While the description of new species is not always the most important part of mineralogical investigation, still these figures serve to show the large part that the Journal has played in the growth of American mineralogy. ”

“ Here also a preliminary knowledge of the elements of geological [64] science will be found very useful, and will frequently enable the traveller to form much more trustworthy conclusions as to the nature and value of mineral deposits than he could without such a guide. But the essential point is to recognise a valuable mineral when seen, and for this some knowledge of mineralogy is requisite.
Outfit.—The essential articles of a geologist’s outfit are neither numerous nor cumbrous. ”

“ One of the results of the progress of science has been gradually to make less distinct the lines that separate the three kingdoms from one another, so that we are led to the conclusion that the mineral kingdom is connected by successive degrees with the vegetable and animal kingdoms, and consequently that matter is one.
Hence the study of mineralogy, giving the word its real signification of a science applying to all unorganized bodies, ought to precede the study of botany and zoölogy, because it is the rational introduction to knowledge respecting the phenomena of Nature. ”

“ Other sedimentary rocks consist of minerals deposited from solution either by chemical or organic agencies, from sea-water, lakes or springs: e.g. the calcite of limestones, deposits of bog-iron-ore (limonite) , gypsum, rocksalt, &c.
Minerals Segregated in Veins and Rock-cavities.—Water percolating through rock-masses takes up mineral matter in solution, and the solutions so formed may further react on the minerals composing the rocks. ”

“ In gneisses and crystalline schists, quartz, felspar, mica, talc, amphibole, &c. are important constituents.
Minerals of Sedimentary Rocks.—By the weathering and disintegration of igneous and metamorphic rocks the various minerals set free and the products of decomposition of others supply the material of sedimentary rocks; thus sandstones consist largely of quartz, shales of kaolin and other clay minerals. Those minerals (e.g. gem-stones and gold) which resist the action of weathering processes are found as water-worn pebbles and grains in detrital deposits. ”

“ I need not point out the difficulty of reconciling such a supposition to the general theory of mineral species and of definite proportions, since mineralogists are already aware of it, and since many other cases, attended by similar doubts, are well known. It is a question too important to be discussed without much more numerous and better established facts than those which we yet possess, and it will hereafter become an object of serious investigation to mineralogists, when their science shall have made further progress. ”

“ We now approach the study of the natural history of the globe, aided not only by the higher branches of Physics, but by still more essential recent discoveries, in Mineralogy, and Chemistry, in Botany, Zoology, and comparative Anatomy. ”

“ All the known chemical elements have been found in minerals; and of many of them minerals are the only source. On the other hand, nitrogen, which is frequently present in organic substances, is rare in minerals; carbon has a wide distribution in mineral carbonates. It is estimated that the minerals of the earth's crust consist of about 47% by weight of oxygen, 27 of silicon and 8 of aluminium; silicates, and especially aluminosilicates, therefore predominate, these being the more important rock-forming minerals. ”

“ In other cases there may be no evident chemical relationship between the two minerals, as, for example, in pseudomorphs of native copper after aragonite or quartz after calcite. Different minerals may also take the form of various organic remains.
III.—Nomenclature and Classification of Minerals.
A mineral species, or simple mineral, is completely defined by the statement of its chemical composition and crystalline form. When we are dealing with a definite chemical compound the limitation of species is easy enough ”

“ These masses have fallen from the cliffs above, and lie detached on the shore. They consist principally of a confused crystallization, but cavities are also found in them in which the mineral has crystallized at liberty and in its regular form. These crystals exceed a quarter of an inch in length, and the substance is here invariably of a white colour. There is nothing more remarkable in this mineral than the contrast between its present and its original state with respect to hardness. ”

“ Much of the physical history of the compound forms of unorganized mineral bodies, has been anticipated in the considerations given in our early chapters to the unstratified and crystalline rocks. It remains only to say a few words respecting the simple minerals that form the ingredients of these rocks, and the elementary bodies of which they are composed. ”

“ Bentley, Serm. vi. of Atheism, p. 192.
↑ The term simple mineral is applied not only to uncombined mineral substances, which are rare in Nature, such as pure native gold or silver, but also to all kinds of compound mineral bodies that present a regular crystalline structure, accompanied by definite proportions of their chemical ingredients. The difference between a simple mineral and a simple substance may be illustrated by the case of calcareous spar, or crystallized carbonate of lime. The ultimate elements, viz. Calcium, Oxygen, and Carbon, are simple substances ”

“ This is far from being the only case in nature where mere mineral distinctions are insufficient to determine the geological situation of a rock. In the stratified classes of rocks, both primary and secondary, these resemblances are frequent, since it is often impossible to distinguish quartz rock from sandstone, the breccias which it contains from the more recent graywacké, ancient clay slate from recent, or, as I have shown in this very account of Sky, primitive from secondary limestones. ”

“ A mineral is characterized by a constancy of composition and of properties which sets it apart from rocks which vary widely. Minerals may be metallic, like pyrite, or non-metallic, like barite; they may be ore, like galena, or rock-forming, like quartz or feldspar; they may show crystal faces, or they may be fragments with rounded or broken surfaces. A favored definition teaches that “a mineral is a naturally occurring, inorganic substance having a definite chemical composition and definite physical properties, within limits.” ”

“ The mineral composition of rocks is greatly simplified by the wide range of conditions under which the commonest minerals can be formed. Thus quartz, feldspar, mica, the minerals of the hornblende, or pyroxene group, can be formed from a mass cooling from a state of fusion; they may be crystallized from solution, or be formed from volatilized products. They are therefore the 25commonest of minerals and are rarely excluded from rocks of any class, since there is no process of rock formation which determines their absence. ”

“ Under the influence of percolating, heated waters, new minerals are formed in sedimentary or igneous rocks, and rocks once metamorphosed may undergo additional changes. Mineral matter previously widely disseminated through rocks is, under the action of percolating, heated water, brought together and the regeneration and crystallization of a large variety of ores and minerals result. The birthplace of a large variety of ores and minerals is in the zone of metamorphism. It is in metamorphic rocks that the geologist looks for gems, the precious metals, crystalline marble, magnetic iron, etc. ”

“ Or, more specifically, a mineral is a natural, inorganic, homogeneous substance of definite chemical composition. According to this definition a mineral must be found ready made in nature, must not be a product of life, must be of the same nature throughout, and its composition must be so definite that it can be expressed by a chemical formula. All artificial substances, such as laboratory and furnace products, are excluded from the category of minerals. Coal is not a mineral because it is both organic and of indefinite composition. ”

“ The three principal methods by which mineral substances are concentrated, namely, the mechanical, chemical, and vital, have in the main different fields of action. The mechanical and vital agencies operate at the surface of the lithosphere, although organic products, principally certain acids, descend into the earth in solution in water and play an important part in deep-seated chemical changes, as in the formation of mineral veins. The chemical agencies bring about the concentration of mineral substances both at or near the surface and at a depth. ”

“ Before one may gain a knowledge of rocks or the architecture of their arrangement within the earth’s crust, it is quite essential that some familiarity should be acquired with the appearance and properties of the commonest minerals, and particularly those which enter as essential constituents into the more abundant rocks. To be a competent mineralogist, one must have a rather extended knowledge both of inorganic chemistry and of the science of crystallography, which, fascinating as it is to study, involves some technical knowledge of mathematics and much laboratory experience. ”