Name: Discoscaphites conradi

Phylum Mollusca; Class Cephalopoda; Subclass Ammonoidea; Order Ammonitida

Geological Time: Cretaceous

Size: 22 mm (24 mm by 26 mm matrix base)

Fossil Site: Fox Hills Formation, South Dakota

The high degree of preservation of its natural mother-of-pearl shell makes it appear to be preserved as gemstone. This is a consequence of light passing through the various layers of aragonite and conchiolin deposited by the ammonite in life. Conchiolin is secreted by various other mollusks, including oysters, and is a complex protein. The colors change with changing perspective but the dominate green mixed with pink stand out for this little gem. 

Phylum Mollusca; Class Cephalopoda; Subclass Ammonoidea; Order Ammonitida

Geological Time: Cretaceous

Size: 26 mm (40 mm by 78 mm matrix base)

Fossil Site: Fox Hills Formation, South Dakota

The high degree of preservation of its natural mother-of-pearl shell makes it appear to be preserved as gemstone. This is a consequence of light passing through the various layers of aragonite and conchiolin deposited by the ammonite in life. Conchiolin is secreted by various other mollusks, including oysters, and is a complex protein. The colors change with changing perspective. 

Sutures (or suture lines) are visible as a series of narrow wavy lines on the surface of the shell, and they appear where each septum contacts the wall of the outer shell. The sutures of the nautiloids are simple in shape, being either straight or slightly curved.
This is different from the "zigzag" sutures of the goniatites and the highly complex sutures of the ammonites.