Natural Puka Shell Formation
The shell of a cone snail is cone-shaped, and closed at the larger end. When the dead shell is rolled for a long time by the waves in the breaking surf and coral rubble, the narrow end of the shell breaks off or is gradually ground off, leaving only the more 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 considered to be a sort of a natural bead, and is known as a "puka". Real puka shells are not flat: one side of the bead is slightly convex, the other concave. The concave side of the bead clearly shows the spiral form of the interior of the spire of the cone shell.
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