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
