Popular Science Monthly/Volume 29/July 1886/The Development of Minerals

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968333Popular Science Monthly Volume 29 July 1886 — The Development of Minerals1886Julien Thoulet




IN a lecture on "The Life of Minerals," which was published about a year ago, I tried to bring out a few principles which seem to assert themselves as each day's work contributes new facts and suggests new thoughts in science, and which seem to give a general direction to the labors of investigators. These principles were, in brief, that all the laws relating to the mineral kingdom are also applicable to the vegetable kingdom, which is, besides, governed by other laws special to it; all the laws of the vegetable kingdom are valid in the animal kingdom, and it has, besides, its own other special laws. 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. There is manifest in these days an evolution from the sciences called natural toward the physical and chemical sciences, and from the physical and chemical sciences toward the mathematical sciences.

A natural phenomenon is the resultant of multiple actions which make themselves perceived concurrently in its manifestation. It is an equation containing many unknown quantities. There is only one way to resolve it: it is to find a sufficient number of other equations containing the same unknown quantities with different coefficients and exponents, and then to eliminate the unknown elements one after the other. That is the object of experiments, in which man intervenes with his intelligence and his hands to simplify and finally to resolve the problem that he proposes to himself, which is to obtain a complete knowledge of the phenomenon. In every experiment he retains as constants some conditions which he can not wholly get rid of, and limits himself to putting a single variable through its changes. He then makes constant the variable, of which he has just examined the influence, and subjects to modifications one of the other variables which he had previously held as a constant. This work is really the same as to formulate a new equation between different unknown quantities. Every science must therefore rest upon experiment, which alone is capable of leading to the knowledge of the law—that is, to a generalization, and of permitting the student to foresee results. A science which can not generalize or foresee only deserves the name of simple knowledge. Detailed observation translated into minute description is the servant of experimentation, for its task is limited to verification.

The science of inorganic bodies, mineralogy and geology, has been the first to feel the effects of the evolution of the natural sciences toward the exact physical and chemical sciences. Its phenomena present the minimum of complication; it ought, even more than the others, if that is possible, to be founded on experiment, measure, figures, and number.

I have been gratified to find my views on these subjects corroborated by the observations of Professor Mario Pilo, of the Lyceo Balbo in Turin, as recorded in a paper published by him in the "Ri vista di filosofia scientifica," on "The Life of Crystals; or, Outlines for a Future Mineral Biology." This author has collected a large number of results agreeing with the doctrine of the successive and insensible passage from the stone to the animal; and, although I am not in absolute accord with him in all his conclusions, we agree in the most essential points.

These studies are not of yesterday, and, as is the case with many other branches of knowledge, it is hard to go back to the first person who entered upon them. No branch of science is born in a day; but they all come to their growth in the minds of men and of masses of men by a kind of infiltration, or slow and often unconscious accretion. In 1867 M. Bombicci, Professor of Mineralogy in the University of Bologna, became especially interested in phenomena relating to minerals. Some of his experiments in crystallography were of particular interest, and were marked with the stamp of a rare originality of conception. But he treated the problems they suggested with great boldness, and carried his speculations upon them, perhaps, beyond the limits of rigorous science. It fell to M. Pilo's lot not to institute new experiments, but to collect those of M. Bombicci, his master and friend, correct and edit them, prune them of what about them was too technical, and, checking them with new facts duly substantiated, to present them in a more modest aspect, better deserving to attract attention. M. Pilo has given, in a kind of list, the analogies between the organic and inorganic kingdoms, and has concluded from them that there exists a kind of mineral biology. His memoir, aside from its philosophical parts, is a comparative chart of organic biology and mineral biology, and shows that all the branches of studies relating to organic beings can also be applied to minerals.

He begins by defining life as the state of integration of matter when it, departing from the simply molecular condition, arrives at the state of forming complex groups of determined chemical and physical structure, and becomes capable of reacting upon the ambient medium in such a way as to assimilate to itself the elements peculiarly suitable to it. The individual being a determinate chemical compound under a determinate form, the elementary crystal presents all the characistics of individuality, comprising of them, under the name of crystal, all that has been called, with certain differences of significance, the integrant molecule by Haüy, the physical molecule by Delafosse, or the elementary crystalline stitch of the crystalline network by Bravais. I do not think that, even admitting this definition, we have any right to deny individuality to bodies that are called amorphous. It is not becoming to adopt the exclusiveness of the old mineralogy, which assumed to occupy itself only with the minerals existing in the bosom of the earth, and regarded as of its domain salt when it was found in mines, but refused to study the chloride of sodium which was produced in a laboratory. Amorphousness is still only a condition of form, and it would be absurd to give individuality to a gramme of crystallized sulphur, and refuse it when the same gramme of sulphur, having been fused, has been cooled in a vessel of water. The word amorphous simply means not crystallized. Furthermore, the crystalline condition is connected with the amorphous condition by an uninterrupted series of gradations, as has been proved by the labors of Vogelsang and Lehmann. The former of these observers dissolved sulphur in sulphuret of carbon, and thickened it by mixing with it Canada balsam, the viscosity of which caused a delay in the crystallization at the will of the experimenter. By this method he substantiated a grouping of the matter into globulites, or minute isolated spheres; then into margarites, or files of spheres joined to one another. He next produced trichites, which are abundant in the obsidians—a kind of extremely fine threads of mineral, containing an internal channel, and rolling up in the most irregular fashion; microliths, under the various forms of longulites or belonites; and, finally, the crystallites and crystalline skeletons of Lehmann; and these, in their turn, led to real crystals. Each of these states presents itself as a more perfected condition than the one that precedes it, as a new appearance and complication of physical properties. Why, then, abruptly break the chain, and, having recognized the passage from the animal to the plant, and from the plant to the crystal, deny the transition, otherwise very visible, from the crystal to the amorphous body, and pretend that this is only a cadaver? Bodies sometimes crystallize under remarkably slight influences; under prolonged vibrations, as in the wire of suspension bridges; depressions of temperature, like tin; or a simple molecular action, as do arsenious acid and barley-sugar. Glasses, according to the most general opinion, are constituted of an infinite number of interlaced crystals too minute to be distinguished by our microscopes, but which may be forced to arrange themselves in groups, and thus appear visible, by means of a prolonged roasting. In science we must be on our guard against absolutely affirming what our senses do not perceive, but we must be equally wary of supposing that things possess the same limits as the instruments which we are using to-day, but which the ingenuity of an inventor may bring to a greater perfection tomorrow.

In any case, especially if we restrict individuality to the definite chemical compound, the species is more clear in mineralogy than in biology, because it is more simple. The study of the structure of minerals is comparative inorganic anatomy, and, when crystallographers measure angles, refer the infinite variety of different solids to regular geometrical types, and class them in one or another of the six categories of crystalline systems, they perform the work of anatomists. To cite their names would be to write the history of mineralogy over again. We should have to begin with Erasmus, Bartholin, Huygens, and Stenor, and end with the immense number of those who are now engaged with crystallography.

The crystal does not, then, appear suddenly any more than the plant or the animal. It passes through an embryonic state, the general study of which is embryology. And who knows whether the embryology of organic bodies, that science still wrapped in so much darkness, may not be illuminated with an unanticipated light when it shall be able to take for the basis of its investigations the results furnished by the embryology of inorganic bodies? MM. Monnier and Vogt have already imitated, by means of inorganic salts reacting upon one another, the forms of organic cells, and in a work, the summary of which was published in 1882 in the "Comptes Rendus" of the French Academy of Sciences, under the title of "The Artificial Production of the Forms of the Organic Elements," they have examined in detail these extremely delicate phenomena which carry us back toward the elementary origin of beings.

All beings are subject to certain general laws. Experiments in supersaturation show the action of continuity exercised by the parent upon the descendant which resembles it, and the conditions of existence, if not identical, are at least comparable for all. The crystal, in the solution into which it is plunged, increases by taking up, by means of a labor inherent to its nature, the particles which are suitable to it, and which become thus the food upon which it is supported. The struggle for existence is universal. Henri Sainte-Claire Deville announced the application of this thought to the mineral kingdom when, pointing to the iron tubes in his laboratory in which crystals were alternately heated and cooled, he remarked, sententiously, "The large crystals eat up the little ones." All bodies are subject to the action of ambient conditions. Among these incessant variations, these reciprocal influences of the medium upon the being and of the being upon the medium, are certain situations of greater stability, or positions of momentary equilibrium in which the body seems to persist, when an effort, a more considerable change, is needed to displace it. This equilibrium is not absolute. Susceptibility constantly exists, but it is manifested more or less clearly, so that we can define mineralogy as the study of the effects produced by different causes upon minerals. Sometimes a relaxation is apparent, a comparative retardation, a slumber, a lethargy, a catalepsy, a condition of real or apparent death. It is hard to express our idea by using such words as death or destruction, which possess a common acceptation that we are obliged, perforce, to stretch. "If we dry or deprive of heat certain inferior beings, frogs, aquatic insects, or some eggs," says Claus, in his "Zoölogy," "we can interrupt the vital functions for months and years, and still restore the life by returning the water and the heat. While there are some seeds that lose their germinating qualities after a few days, melon-seeds and beans are known to have grown after thirty or forty years, and even seeds of heliotrope and lucern that were found in the Gallo-Roman tombs, and were therefore fifteen or sixteen hundred years old, have been made to grow." The crystal, withdrawn from the mother-solution, and deprived of food, ceases to develop; it continues the same in appearance, although its immobility is not absolute. If the air becomes moist, it falls into deliquescence; if too dry, into efflorescence. It does not possess the same volume nor the same angles in summer and in winter. Still, these changes are relatively slight, and if we take our crystal from the drawer, in which it has been kept inert, and put it in more favorable conditions, it will resume its development. Heated too much, attacked by a strong enough chemical agent, or subjected to any excessive influence, the body will be destroyed, and will experience the more profound modification commonly called death.

May we not also say that there are diseases of minerals? Can we not recognize in some of them a tendency to a healing, or, in other words, to a return toward the state of primitive equilibrium when the cause of the evil has disappeared—provided, always, that the divergence from that position of equilibrium has not been too considerable? We may cite in illustration of this hypothesis the numerous cases of mutilations of crystals that have been studied by Leblanc, Beudant, Lavalle, De Sénarmont, and M. Pasteur, on the bimalate of ammonia ground up in polishing, nitrate of lead, sea-salt, hydrochlorate of ammonia, or crystals of white potash alum, mutilated in certain lines, which, immersed anew in a solution colored with chrome alum, have their wounds cicatrized before resuming their interrupted development—a phenomenon which is made visible by the difference in color of the two isomorphous salts. These curved, twisted, deformed, and monstrous crystals, diverted from regularity by causes most usually unknown, but of which science is on the way toward discovery, would make, in regard to their malformations, objects of a mineral teratology.

The higher the stages of development which bodies reach, the more their forms become complicated; here, again, the chain seems to be uninterrupted. I thought I had substantiated a tendency toward perfection in the curious so-called mimetic appearances which plagiocase feldspar, leucite, analcime, senarmentite, and many other minerals exhibit, phenomena by which many crystals belonging to a more complicated system group themselves in a determined number, so as to offer the deceptive appearance of a single individual belonging to a less complicated system. M. Pilo, on the other hand, sees in this march toward a more simple form a retrogradation, an inverse phenomenon of degeneracy, which he compares to atavism. I yield to his view, and in doing this take notice of one other correlation between the two opposite extremities in the scale of beings. There is also a passage of crystalline systems among themselves, and each property effects this passage separately—a displacement of optical axes which, diminishing their angle, transforms a biaxial crystal to a uniaxial one, successively for each of the colors of the spectrum; an unequal thermic dilatation, positive or negative, following the three axes of elasticity, null in some directions; variation in the mutual inclination of the facets; in the same system, a transition from hemihedral to holohedral forms by sharp grouping in some cases, by striæ like those of pyrites and quartz, of holohedral forms to forms hemitropal in different degrees, and to hemimorphal forms. The complication goes on increasing.

We will end by a last trait of analogy. Just as some animals and plants, when they are by any cause placed in a medium offering the largest sum of propitious conditions, attest the excellence of that medium by a more complete development of the individual and of the number of individuals; as there exists a zoölogical geography and a botanical geography, which distinguishes and enumerates for each species the most favored or most favorable regions—there exists also a mineralogical geography, which fixes the cantonment of particular minerals in certain countries. In the Island of Elba, more than anywhere else, is found oligist iron; in the Hartz and the Ural, ores, and native metals; in India, Brazil, and South Africa, gems and diamonds; in California and Australia, gold; in Canada and Chili, copper; in Siberia, malachite; and in Iceland, Iceland-spar. This study has been elaborated for some substances—tin, for example—in the admirable labors of Élie de Beaumont.

Thus, since we have for minerals an embryology, an anatomy, a nosology, a teratology, and a geography, a vast assemblage of facts many of which are known and more unknown, we may also conclude upon the existence of a mineral biology. When every one of the chapters which it embodies shall have been treated experimentally, we may come into a condition to formulate its laws. The artificial barriers raised by our ignorance between the different branches of knowledge will one after another be leveled. Natural history will become easy, like physics and chemistry, now that physics and chemistry, as Lagrange foresaw, have become easy; or, rather, all the sciences will be consolidated into one science, which will be one because matter, the object of its investigations, is one. Every time the mind of the investigator escapes beyond the work of detail which he daily performs in his laboratory, the contemplation of an ideal far removed, but which he is certain he or those who will follow him will attain, gives him new strength to go back to that daily labor, marks an advance, infinitely little but certain, toward that ideal. A glance over its history shows how mineralogy has grown. It seems as if it were conscious of the end toward which it is tending, of connecting the sciences called natural with the exact sciences. As M. Pilo has happily remarked, mineralogy has traversed the period of magic with the alchemists, the empiric period with the experimenters of the seventeenth century, the naturalist's period with Linnæus, Buffon, and Werner, the geometric period with Haüy, Delafosse, and Bravais, the chemical period with Berzelius, and the physical period with Fresnel, Mitscherlich, and De Sénarmont. It is now time for it, gathering up the scattered results it has collected, and adding new conquests to them, to enter resolutely into the biological period.—Translated for the Popular Science Monthly from the Revue Scientifique.