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
Consequences of the attack on Pearl Harbor into the war at a time when he had not yet acquired full control of continental Europe — on the very day of the Pearl Harbor attack, Hitler himself had issued his Nacht und Nebel decree, concerning the suppression of resistance activities within Nazi-occupied lands. Hitler, who had previously declared the Japanese "Honorary Aryans" claimed that "this is what happens when your allies are not Anglo-Saxons". However, he decided war with the United States was unavoidable, and the Pearl Harbor attack, the publication of Rainbow Five, and Roosevelt's post-Pearl Harbor address, which focused on European affairs as well as the