Popular Science Monthly/Volume 45/September 1894/The New Mineralogy

From Wikisource
Jump to navigation Jump to search



MINERALOGY, as the observation of minerals, is of very ancient date, but such observation was very crude, for the old scholars grouped under one name a great variety of forms, some rocks and some minerals. The earliest writer was a Greek by the name of Theophrastus, who lived about three hundred years before the Christian era. A few centuries later the great naturalist Pliny recorded a number of personal observations. Then followed a blank period extending into the eleventh century, when Avicenna made his mineral classification. In this, the first classification, all minerals were divided into four groups—stones (= silicates), salts, inflammable bodies, and earths. In the next six centuries the only improvement was the substitution of term metals for earths. Through all these many years, it was the beautiful in form, luster, and color of the gems which attracted the attention of men both learned and ignorant. The question of origin was not considered; indeed, it was sacrilegious to think of such a problem, since these were objects of creation, whose genesis, like that of the gods, was not to be revealed to man. It was the work of many centuries to dispel these clouds of ignorance and superstition which blinded and hindered the advance of this study. The only light which did appear was that of the alchemists, those wizards who vainly searched for the lucky stone which would transform all into gold. From the ashes of their fires comes as a heritage the application of heat and fusion to aid in investigation, but even the value of these was not clearly seen for several centuries thereafter.

Behind the clouds there was a light, and the time at last came for it to melt these away, revealing a vast new field for thought and study in the inorganic world. Men began to look more carefully at the objects near them, to observe the ways of Nature, and to attempt the solution of some of her mysteries; then it was seen that even in the inert stone there was a story to be read—an ever-changing story full of historical interest, if only one could read it.

It is interesting to note through these centuries the struggles for existence and advancement which finally brought forth, at the beginning of our era, mineralogy as a science. In the sixteenth century the work of Agricola laid the foundation for physical mineralogy. In the eighteenth century Cronstedt pointed out the distinction, so long unknown, between rocks and minerals, based on chemical properties. At the beginning of the nineteenth century came the work of Werner and Hauye. These men perfected the methods and made more accurate descriptions of minerals, thus becoming the founders of modern mineralogy, and making their respective countries, Germany and France, the centers for this study. During the present century the growth has been as rapid as it was slow during all the preceding centuries, so that at the present time its students nearly outnumber the species.

The study of the properties of minerals—physical, chemical, and optical was carefully made and verified over and over again, but the question of origin was unsettled; in many cases it was even impossible to conjecture. So its devotees sought a means of revealing and proving this problem of origin, and then arose what we may term the new mineralogy. Germany and France have equal share in the honor of founding the science of mineralogy, but to France belongs the credit of original active investigation into the origin of minerals. This feature of new sciences is becoming quite prominent, and one would infer that there was a very great awakening in the scientific world, for we hear of the new astronomy, the new chemistry, and the new geology; but it is not so much new science, as old science studied by new methods brought about by the great underlying law of the universe, progression, which causes the new of to-day to become the old of to-morrow. The new mineralogy endeavors to solve the problem of origin by the reproduction, artificially, of the mineral using similar agents and like conditions, as in Nature. While attempts were made to reproduce minerals early in the century and even near the end of the preceding one, the important work has been done since the year 1850, which date may be taken as the beginning of synthetic mineralogy. Through the eighteenth century came many suggestions on the artificial formation of minerals, followed by the crude attempts at the reproduction of petrifactions and incrustations. Unsuccessful attempts finally led to the successful reproduction of marble by James Hall in 1801, the first mineralogical synthesis and the beginning of experimental geology.

The first workers, as would be expected, were chemists; among whom Daubrée stands pre-eminent. When the mineralogists joined in the work, it was found that the conditions governing the chemist's experiments differed from those they could apply. It was early discovered that the forces at work in the formation of minerals escaped the observation of the mineralogists, and, though observed, were considered outside the domain of chemistry. The chemist's aim was to form a mineral like the one found in Nature; but the mineralogist, in addition, must use analogous processes to. those in Nature. In the chemical sense if the artificial product had the correct chemical composition, reaction, physical properties, such as density, boiling point, and the like, the synthesis was complete. On the other hand, in the mineralogical sense there must be also an entire agreement of the resulting product with the natural one morphologically. It must have the crystal form and also the characteristic type as in Nature, with the same optical properties, in order to be perfect. Thus the chemist could deposit copper by electrolysis, like the copper found in Nature; but this does not show the origin of copper in Nature. His task is the easier one, for he uses his reagents at pleasure, aiming only at the final product. In the course of time, the chemist and mineralogist seeing their mutual needs, united their efforts, and it is on this union that mineral synthesis as a science rests.

The cause of the long delay in the progress of this line of study was the idea, so firmly fixed in the minds of the old chemists, that Nature worked by mysterious means and had at her disposal indefinite time and enormous masses with supposed forces out of all proportion to those used in the laboratory. Then how was it possible in a crucible with a certain number of grammes of matter to reproduce a crystal of the same kind and association as those which the volcano ejected—a crucible a million times larger and under enormous pressure and temperature? The answer seemed too clear to even admit of such a vain attempt; they could not see the law of proportion which existed there, but it only needed progressive men to discover it. Even when this law was discovered, the crude means and limited experience at hand retarded them and made the progress very slow down to the middle of the present century.

At the beginning of the cycle there existed the two opposing geological camps, the one attributing everything to fire, the other all to water; after long years of wrangling their union was accomplished through the efforts of Lyell and his followers. In addition to this, the accumulating observations overthrew two old ideas—namely, that a mineral can only originate in one way characteristic to it, and a single homogeneous magma can give rise to only one mineral. It was found that a mineral may originate under different conditions which are determinable, and that the homogeneous magma may at the same time give rise to different minerals. The various mineralogists appeared to take pleasure in throwing an envelope of mystery around the origin of minerals, and they were regarded, even by Zirkel, as the work of a kind of vital force.

Practical difficulties deterred the progress of the study; the crystals formed were sometimes imperfect and usually microscopic. So it was almost impossible to study them before the development of mineralogical micrography and the advent of the mineralogical microscope. Then it was found that these minute imperfect crystals were of more value and led to greater results than the more beautiful cabinet specimens, for they settled the problems of origin. Natural crystals were found to contain small inclusions which are indices to the origin. If these are vitreous, then the origin is vitreous, and the action of volatile agents is wholly excluded; if these be aqueous, the intervention of water is indisputable. In certain minerals—as quartz, beryl, topaz—liquid carbonic acid appears as an inclusion, giving evidence of their formation under great pressures.

From this brief survey we see the strong prejudices of the ancients are disappearing; observation and the processes of investigation have acquired a remarkable precision; materials and apparatus in the laboratories have been perfected to a remarkable degree.

Under the head of artificial minerals we exclude those accidentally formed in the industrial works, as graphite on the walls of iron furnaces, for such do not answer the question of their origin, since the reagents and conditions remain unknown. Nevertheless, the recorded observations of such products have aided reproduction in the laboratory, and it is of interest that these observations have been noted especially by German workers, while the home of active laboratory investigation is in France. The Germans collected the facts, while the French co-ordinated them, forming hypotheses and then experimenting to prove them. The Russians followed with almost equal success; also much important work has been done in the laboratory by the Germans.

The practical side of a subject must always be considered, the question of utility being a very important one. What claim has this subject for attention and what has it accomplished? It has thrown light on the mode of the natural formation of minerals and rocks. Thus even down to late time water was thought to play an important part in the formation of a great number of volcanic rocks and to be indispensable in the formation of the great group of rocks termed basalt. Yet basalt and all the modern volcanic rocks have been formed by purely igneous fusion. Again, certain minerals—as chiastolite, garnet, staurolite, and a large number of metamorphic minerals—are always found impure in Nature, and their exact composition was unknown until reproduced artificially. The majority of natural minerals are complex combinations in which many bodies are introduced by isomorphous agency. Synthesis has furnished the theoretical types and given forms which could be accurately measured and show the true physical properties.

Mineral synthesis determines the individuals belonging to a family and distinguishes the true isomorphism of the series in question. The artificial reproduction of the feldspar series proved that the two members, albite and anorthite, were isomorphous and could be united in all proportions, some new forms being found which were unknown in Nature. Other mineral types which are suggested by, but are absent in Nature have been formed artificially, thus completing a mineral series, making the limits of isomorphism more clear. This was accomplished by Ebelmen in the spinel family, showing the relation of ferrites, chromates, and aluminates to each other; also by Foque and Levy in the feldspar family, who formed new feldspars with bases of lithia, barytes, strontium, and lead. This work has also been of great assistance to geology, a science which has been encumbered by theories and hypotheses, where observation was in very many cases insufficient to settle definitely the doubts. Synthesis, when applied, enlarged the field of observation and so often furnished definite solutions. Thus the origin of granite was one of the great problems confronting geologists. The opinion that it was purely igneous prevailed in the science for the first part of our cycle, replacing the Neptunist or aqueous theory of Werner, but the difficulties were increased a little later when, by means of the microscope, it was found the quartz was consolidated after the other minerals; this was against the idea of a purely igneous fusion of the granite. The upholders of this theory then argued for an extra fusion of the quartz analogous to sulphur. Élie de Beaumont in 1849 modified the theory by admitting the intervention of water. For proof he called attention to the number and frequency of the minerals sublimed on the periphery of the massive granites. He thought the water occurred in the form of inclusions in the granite constituents, which was proved ten years later by Sorby. From this time on there was the new theory for a mixed origin of granite. When synthesis was applied it was found impossible to obtain granite by purely igneous fusion.

The new mineralogy has accomplished much and has extended our knowledge of rocks and minerals far beyond even the dream of its founders, so that to-day nearly all known rocks have been formed artificially with the same minerals and under the same associations as in Nature. Of the different mineral species but very few remain which have not been reproduced in the laboratory, and each year decreases this number. The only ones which have not been reproduced are epidote, allanite, zoisite, staurolite, disthene, andalusite, and tourmaline, a very small number, which will probably be removed in the next few years. All this work has been accomplished in a comparatively short period of time in three countries, France, Russia, and Germany.

Thus we see the new mineralogy has given breadth to the old and has established a better foundation on which to build, since it has disclosed the long-hidden mystery of the origin of minerals and rocks.