Chalcedony is a type of quartz. It comes in many colors and is sometimes dyed. Some varieties are agate, carnelian, chrysoprase, heliotrope and onyx.
Briolettes are usually teardrop, triangular or pear shaped gemstones that have a hole drilled horizontally left to right across the top of the stone. Sometimes they are faceted. They range in size from tiny (4-5 mm) to very large (25 mm).
Here is a picture of a piece I made with yellow creme chalcedony briolettes and purple freshwater pearls.