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
The Pearl (novel) his head blown off in the pearl, throws it into the ocean. Steinbeck began writing the story as a movie script in 1944, and first published it as a short story called "The Pearl of the World" in "Woman's Home Companion" in December 1945. The original publication is also sometimes listed as "The Pearl of La Paz". He expanded it to novella length and published it under the name "The Pearl" by Viking Press in 1947. As he was writing the novella version, he was frequently travelling to Mexico where the film version, co-written with Jack Wagner, was being filmed.