Noun
English Wikipedia has an article on:conchiolinWikipedia
conchiolin (plural conchiolins)
(biochemistry) Any of a group of proteins which, together with polysaccharides and calcium carbonate, make up the shells of molluscs.
The mollusk, irritated by the intruder, forms a pearl sac of external mantle tissue cells and secretes the calcium carbonate and conchiolin to cover the irritant. Source: Internet
With X-rays it is possible to see the growth rings of the pearl, where the layers of calcium carbonate are separated by thin layers of conchiolin. Source: Internet