Jewelry consisted of small decorative accessories worn for personal adornment. They could consist of gemstones, precious metals, and/or other hard materials.
In 2367, attempting to retrieve his commbadge, a disguised William T. Riker asked Berel about it, describing it as "jewelry, a metal pin". Berel replied that he hadn't found anything other than the phaser Riker possessed (which the officer passed off as a toy.) (TNG: "First Contact")
In 2370, the Barkonian blacksmith Skoran created jewelry from radioactive metallic probes without knowing that these pieces were causing radiation sickness. (TNG: "Thine Own Self")