Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
SEM view of a fracture of the calcitic prismatic layer of Pinctada margaritifera. The outer shell surface is at the top and prisms grow to the shell interior (downwards). During shell growth, many small prisms disappear, whereas the surviving units increase in size. Note organic walls surrounding prismatic units, particularly well preserved in the upper part of the layer.
