Puka shell

from Australia The terminal helix of the shell of a cone snail is cone-shaped, and closed at the apex. When the empty shell is rolled over a long time by the waves in the breaking surf and coral rubble, the terminal helix of the shell breaks off or is gradually ground off, leaving the solid top of the shell intact. Given enough time, the tip of the spire of the shell usually also wears down, and thus a natural hole is formed from one side to the other. This shell fragment can be viewed as a sort of a natural bead, and is known in Hawaii as a "puka". Real puka shells are not flat: one side of the bead is slightly convex; the other is concave. The concave side of the bead clearly shows the spiral form of the interior of the spire of the cone shell. ==Modern substitutes==

Naturally-formed rounded cone shell fragments suitable to be used as beads are hard to find in large quantities, so true puka jewelry, formed entirely naturally, is now uncommon. Shell jewellery made from naturally occurring puka shells is also now more expensive because of the labor and time involved in locating and hand-picking these rather uncommon shell fragments from the beach drift. In modern times, beads cut from other types of shell, or even beads of plastic, are used to make imitation puka jewellery. Cone snail shells are sometimes harvested so that they can be chipped and ground down to make more authentic-looking puka jewellery, which is however still not genuine by the standards of the originals. A very glossy patina indicates that the shells in a necklace have been tumble polished. If the edges of the shell beads are chipped, the shells were harvested and manually broken into shape. If the "puka" or central hole is perfectly circular and parallel-sided, then the hole was drilled by humans. ==See also==