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
Daniel Pearl On December 10, 2007, President George W. Bush and Laura Bush invited Ruth and Judea Pearl, parents of Daniel Pearl, to the White House Chanukah reception. They lighted the Pearl family menorah that once belonged to Daniel's great-grandparents, Chaim and Rosa Pearl, who brought it with them when they moved from Poland to Israel in 1924. There they helped establish the town of Bnai-Brak. The late former mayor of New York City Ed Koch requested that his own tombstone be inscribed with Pearl's words: "My father is Jewish, my mother is Jewish, I am Jewish." Shortly after Pearl's death, his