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 of Death The Pearl of Death The Pearl of Death is a 1944 Sherlock Holmes film starring Basil Rathbone as Holmes and Nigel Bruce as Dr. Watson, the ninth of fourteen such films the pair made. The story is loosely based on Conan Doyle's short story "The Adventure of the Six Napoleons" but features some additions, such as Evelyn Ankers as an accomplice of the villain, played by Miles Mander, and Rondo Hatton as a brutal killer. Master criminal Giles Conover (Miles Mander) steals the famous "Borgia Pearl" from the Royal Regent Museum under the very nose of Holmes and Watson, but