It is difficult to determine the provenance of shell buttons with certainty. If anyone has specific information on this subject, please contribute. Additionally, they do not scan well, as colors are muted and vary in subtle shades of white.
Freshwater mussels are the most likely source for those on the left, above, and further contrast-enhanced left, based on the presence of a pallial line structure visible within the nacre in some. The sheen is silvery, and the play of diffraction colors is almost absent in most freshwater shell.
Many of those in the center, above, show a white layer with pinkish markings. Others have nacre identical in color and texture with those with markings. Color is somewhat yellowish, diffraction colors are stronger and "grain" is more uniform. These may come from a marine turban shell, Trochus niloticus L., 1767.
Finally, the majority of buttons, above right, come from unidentified sources which may include the thinner nacreous parts of freshwater mussel shells, marine mussels, pearl oysters, jingle shells, and a variety of other species. Some are gray and relatively opaque. The two small ones at the bottom of the assemblage are characterized by a distinctive linear structure within the grain of the shell.