Bead

Beads can be made from a variety of materials (glass, wood, bone, ivory, gemstones, coral, metals, and more obscure materials) and into a variety of shapes.

Medieval beads are often well smoothed and neatly worked - modern gemstone chips would probably have been considered inferior products. Some fine filigree wire beads are known from parts of the period, especially from the byzantines, colourful intricately patterned lampwork glass beads are especially associated with the vikings, and tiny glass seed beads with late period venice. Beads could even be carved into elabourate shapes.

Beads could be used for a wide variety of purposes. Not simply strung as necklaces, beads made other pieces of jewlry, but were also used to adorn clothing, decorate embroideries, etc. Rosaries or paternosters were strings of beads used to count the number of prayers to be said by the catholic faith in period, and were a common acessory at all levels of society. Prayer beads were used in some other religeons including islam.

More info:

• Lois sherer "50,000 years of beads".
• Rosaries and Paternosters