Pearl or parasite enters a bivalve mollusk and settles inside the shell. 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. This secretion process is repeated many times, thus producing a pearl. Natural pearls come in many shapes, with perfectly round ones being comparatively rare. Typically, the build-up of a natural pearl consists of a brown central zone formed by columnar calcium carbonate (usually calcite, sometimes columnar aragonite) and a yellowish to white outer zone consisting of nacre (tabular aragonite). In a pearl cross-section
Pearl of Csaba and Bulgaria. Pearl of Csaba Pearl of Csaba ("Csabagyöngye" in Hungarian) is a white variety of grape. It was created in 1904 by the Hungarian viticulturalist Adolf Stark, presumably by crossing Madeleine Angevine × Muscat Courtillier (= Muscat Précoce de Saumur). Some sources instead state the parent varieties as Bronner x Muscat Ottonel, but this is seen as less likely. The variety's name was taken from the city Békéscsaba, which is also called "Csaba" for short. Pearl of Csaba is primarily used as a table grape. Worldwide cultivation is estimated to be around , and it is primarily found in