Guitar plectrums / picks were originally made of tortoise shell. Today, they are made of all kinds of natural and artificial materials as well as variety of shapes.
D'Addario Guitar Pick - Casein - 351 Shape Shell 2.0mm - Single Pick
D'Addario Guitar Mandolin Pick - Chris Thile Signature Pick - Casein - Triangle 1.4mm
D'Addario - Planet Waves Guitar Picks 10 Pack Duragrip 1.5mm Super Grip