Nacre is made of two substances, aragonite -- which is translucent, giving the pearl its beautiful lustrous appearance and conchiolin -- which acts as a glue holding the layers of aragonite together.
The shell consists of an organic basis the substance of which is called conchiolin, impregnated with carbonate of lime, with a small proportion, I-2%, of phosphate of lime.
Typical albuminoids are gelatin, keratin, elastin, fibroin, spongin and conchiolin.