adventurescence and adularescence and nacreous and pleochroic

In the last essay I argued, among other things, that the general "rainbow-term" iridiscence has been supplemented in recent days by labradorescence, even though opalescence, which at one time seemed to have imperialistic ambitions, has retreated to mean no more than a "milky" iinterior sheen. In this essay we will see how other terms collapse in meaning or, better said, are associated with only one underlying mineral. Let's begin, however, with the general term pleochroism.

Pleochroism

The OED defines pleochroic as "showing different colors when viewed in two or in three different directions (dichroic and trichroic are the more specific terms), as certain double-refracting crystals." Pleochroic minerals show their different colors depending on what direction the viewer is observing the crystal. Some minerals only change minimally, but in some the color change can be dramatic. Pleochroism is caused by the absorption of different wavelengths of light travelling through different directions in the crystal. Andalusite goes from yellow-green to red-brown when looked at from different directions, and Kunzite goes from pale to dark pink. Freeing the term from gemology might be desirable. Thus, we could possibly look at the patriarch Joseph's "coat of many colors" as his "pleochroic coat."

Nacreous

This was always a word I thought I should know, but I never seemed to learn what it meant. Something that is nacreous is, according to the OED, "a smooth, shining, iridescent substance forming the inner layer in many shells; mother-of-pearl." Webster's 1913 dictionary, which is now online, defines it as "having a play of lustrous rainbow-like colors." There can be "nacreous (or pearlescent) clouds looking like mother-of-pearl." Oops. Let's not get started with pearlescent though, in fact, its definition is crystal clear, so to speak. Then, the 1913 dictionary goes on to define it as "a milky opalescent (or opaline) luster." Finally, it provides the following synonyms: "bright, iridiscent, opalescent, opaline, pearlescent." Well, you just have to know that nacreous refers primarily to the colorless inner shell which can be dyed nearly any color.

Adularescence

This word doesn't appear in the OED, but adularia does. Adularia is moonstone, a variety of orthoclase, which is one type of feldspar. So, adularescence is the kind of light emitted by a moonstone. A moonstone is either transparent or translucent with a "pearly" or "opalescent" luster--there are those words again. The Larousse Encyclopedia has it that moonstone gives off its distinctive hue because it "consists of alternating parallel planes of potassium-rich (orthoclase) and sodium-rich (albite) feldspars....The thinner component layers are smaller than visible wavelengths and scatter light, creating a nacreous or silvery appearance, with a bluish sheen called adularescence." It is called moonstone because the sheen is reminiscent of lunar light, especially when the stone is cut into convex, round stones, called cabochons.

Thus, we might be able to differentiate opalescence from adularescence and nacreous in that the first is a "milky" or "cloudy" or "foggy" substance, the second is a "moon-like" substance and the third is more "pearly," but I don't know if anyone will want to hold me to this kind of specificity in definition.

A(d)venturescence

This is another word that doesn't appear in the OED but is derived from the Italian l'avventura, meaning "by chance." When inner platelets are randomly oriented in a stone to give it a sparkling flash, we say that shows forth a(d)venturescence. It, too, is derived from a particular mineral--aventurine--which is a cryptocrystalline quartz contining inclusions of small crystals that reflect light. Adventurescence is a speckled appearance in the stone, and the most valuable color of aventurine is green. It is often confused with jade.

Conclusion

Shimmering, glistening, gleaming, glowing. We have synonymns galore to try to capture the indescribable energy, beauty and brilliance of nature. If only our words could be "asymptotic" words, that is, words that are tangent to the phenomenon at infinity, words that actually "touch" the thing which they describe. But, words can only approximate and must constantly be referred back to the stone or the color pattern they describe. The play of colors shows us once and for all the limitation of the play of our words. But, nevertheless, the words are useful, and helpful, and potent. Attempts to use them can bring a richer appreciation of the stone or phenomenon to us because the word supplies sound. Thus, iridescence not only communicates a rainbow but communicates a flowing and beautiful sound. That, ultimately, might be the value of the words.