Metals and precious stones usually lie with their first seeds deep down in the earth and require continuous moisture and a mild heat. This they obtain through a reflection of the sun and the other stars in the manifold movement of the heavens.... Therefore, also, the metals and precious stones are nearest related to the planets and the stars, since these influence them most potently and produce their peculiar qualities, for they are enduring and unchangeable and show therein their concordance [with the stars and the planets].[441] Hence it is that the influence over human fortunes ascribed by astrology to the heavenly bodies is conceived to be strengthened by wearing the gem appropriate to certain planets or signs, for a subtle emanation has passed into the stone and radiates from it. A combination of several different stones, each partaking of this special quality, was believed to have an influence similar to that exercised by several planets in conjunction,—that is, grouped in the same “house” or division of the heavens. The same is true of the stones dedicated to the guardian angels; the color and appearance of the stone was not merely emblematic of the angel, but, by its sympathetic quality, it was supposed to attract his influence and to provide a medium for the transmission of his beneficent force to the wearer. The whole theory, whether consciously or unconsciously, rested on the idea of harmony, of the accord of certain ethereal vibrations, either those of the visible light of the stars and planets or the purely psychic emanations from the spiritual “powers and principalities.” The wearing of the appropriate zodiacal gem was always believed to strengthen the influence of the zodiacal sign upon those born under it, and to afford a sympathetic medium for the transmission of the stellar influences. The gem was thus something more than a mere symbol of the sign. The same was true of the stone of the saint who ruled the month and that of the holy guardian angel set over those born in the month. In each and every case the material form and color of the stone was believed to attract the favor and grace of the saint or angel, who would see in the selection of the appropriate gem an act of respect and veneration on the part of the wearer.