Star of David or Seal of Solomon. Possibly a symbol of Pythagorean origin. It is formed by two opposing equilateral triangles, one inside of the other. It represents the universal balance between opposites.
Nacre (also called mother of pearl), is an organic-inorganic composite material produced by some molluscs. It is a hard, shining, iridescent material. It is formed in the inner shell of some of the more ancient lineages of bivalves, gastropods, and cephalopods to repair their damaged shells or to cover some objects inside of them. This is used by some pearl pickers, placing certain small items inside molluscs, knowing they will be covered in nacre, forming pearls or other valuable objects. The molluscs that produce the most beautiful nacre are the Abalone and the Nautilida, among other. Nacre is used in medicine for skin care, as an exfoliant.