Shell Disk Bead

A shell disk bead is a small, flat, round bead cut from the wall of a shell and drilled through the center. Sizes range from tiny disks about 2.5 mm across and under 1 mm thick to large disks about 50 mm across, but most are a few millimetres to about 10 mm across. Faces may be flat or keep the shell's curve, and edges are straight or slightly rounded (Holmes 1883; Donaldson and Wortner 1995).

Blanks were broken or sawn from the walls of marine shells, such as whelks (Busycon) and hard clams, or from freshwater mussels, then ground round and drilled, usually from both faces so the hole is biconical (Holmes 1883; Kozuch 2003). At Cahokia, bead makers used tiny chert microdrills, whose wear shows they were used on shell, and workshop areas at Kunnemann Mound and Ramey Field yielded microblades, a sandstone saw and unfinished beads (Kozuch 2003). On California's Channel Islands, Island Chumash drilled Olivella shell disks with microdrills of Santa Cruz Island chert (NPS).

Holmes (1883) describes shell beads used as personal ornaments, as currency and as memory records. Disk beads are common in village middens and burials. The key trait is a small flat disk of shell wall, ground round and drilled through the center.

Diameter about 2.5–51 mm and thickness about 0.8–13 mm (Holmes 1883, converted from inches). Glacial Kame disk beads in Ontario measure 3–11 mm across and 1.5–3 mm thick (Donaldson and Wortner 1995).

Throughout North America wherever marine or freshwater shell was available or traded: Atlantic and Gulf coasts, the Mississippi Valley and Southeast (especially Cahokia and other Mississippian centers), the Great Lakes, and the California coast and Channel Islands (Holmes 1883; Kozuch 2003; NPS).

Shell shows fine growth layers on the edge and may keep the shell's curve; Holmes (1883) took irregular biconical holes as a sign of hand manufacture. Columella beads are cut from the central column of a whelk and are barrel- or tube-shaped rather than flat; at Cahokia, Moundville and Spiro over 90% of columella beads come from left-handed (sinistral) whelks, probably from Florida's Gulf coast (Kozuch 2003). Whole small shells pierced for stringing, such as Marginella and Olivella, form a third bead class (Holmes 1883; Kozuch 2003). Stone and bone disk beads have the same shape, so check the material. Yerkes' microwear work, cited by Kozuch (2003), showed that Mississippian microdrills were made for drilling shell.