There are quite a few loose ends left hanging on my blog already: things I said I will do, questions I had asked. Let me follow up with some answers to my call for an appropriately novel name for the origin of pearls and for better "muscle pearls" like this one:
To begin with, my call to "name the origin of pearls" brought in new wording to consider: natural pearl 'initiation' for the relevant process leading to the formation of natural pearls, and natural pearl 'cores' for the often distinctive material deposited at first.
At least to my ears, the two words are fresh enough to serve old and new ways of thinking on the subject just as well. 'Initiation' sounds particularly appropriate to this context of soft matter, much less dubious than Jameson's quaintly interventionist "agency", certainly less ambiguous than my former choice of "natural pearl nucleation" borrowed from the dictionary of the other industry of pearls… Then, any of the innermost regions of all the natural pearls that I have opened do fit fine in the category of 'stuff in the middle', that is to say, 'cores'. Long story short, I will be initiating natural pearl cores—so to speak—until there’s reason to call them by any other name.
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Turning to a second loose end—I have mentioned 'muscle pearls' with more enthusiasm than pearls to show (with these small exceptions); let me rectify:
Much to be said! Although I have mentioned these already in KEM, I am very tempted to dedicate a paper to muscle pearls, especially if samples comparable to Jameson's incredibly lucky find* do get into the Centro de Instrumentación Científica here at the University of Granada. I would be merely replicating an old—if fabulous—observation. Please do take my word for it that more can be seen in such samples now than back in the day. These things seem to take time—my call for samples is receiving answers often, along the lines of 'still no muscle pearls from this dive'… I am certainly getting a sense of how rare natural pearls are!
Yet, it so happens that a couple of muscle pearls have been sitting in my drawer all along—in fact, they are also posted on this blog already, if rather by coincidence, in the first image posted on May 16: please squint for the small whites lodged into the rough, dull patch—where the great adductor muscle once got itself attached to this Pteria sterna shell. I mention often the ever interesting group of eighty free pearls developed in this shell—in fact, their beautiful cores are right now on my desk shortlisted as subjects of interest; it so happens that the pearls embedded in the muscle attachment have only just beckoned while the images above were being shuttled through email. I do not seem to have any great option to take a better look at these embedded pearls without wrecking that shell… So be it. The "loose end" on these muscle pearls remains, although it looks somewhat less loose. Will, indeed, follow up.
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To sum up the list of loose ends due: I ought to catch up with the color of golden pearls, with the clear brightness of foliated calcite, and with the subtle flame patterns of pearls built of fibrous aragonite—ripe for an unhoped-for summer of photography. At least the last two topics bring me to a handful of great writing in gemmology by C.V. Raman—some mentioned in my paper and in my writeups sent to Pala International's newsletter before this blog.
* Pearl-Oyster. See page 272, and plate XXXV at page 352; more examples of "nacreous muscle-pearls" at page 324, in H. L. Jameson, Studies on Pearl-Oysters and Pearls. -I. The Structure of the Shell and Pearls of the Ceylon (Margaritifera vulgaris Schumacher): with an Examination of the Cestode Theory of Pearl Production, Proc. Zool. Soc. London (1912).