This is a 15in strand of dark blue polished goldstone glass beads, identified by the Persian name "Sitara".
Not a natural mineral at all. Not gold either. Goldstone was the result of a happy accident. A medieval glass maker in Italy or Persia (depending on who you ask) accidentally dripped copper into molten glass, left it sitting in anaerobic conditions, cooled it, and then decided to carve it. Thus goldstone was born.
Once discovered, this special glass was used to create carvings and inlays, since it was easy to work. The glass with the uniform star-like glitter effect was called aventurine glass. To achieve the effect, the artisan needed to include other metal oxides in with the copper to reduce it to its elemental state - an early chemistry experiment for those times.
Different metals would render differently colored glass. The standard color, clay red, came from copper. Cobalt would result in a deepest blue, then purple glass from manganese, and green glass from chromium oxide. All exhibit the lovely aventurescence from evenly formed metal crystals in suspension. Nice to gaze at, smooth to touch when polished.
These dark blue goldstone beads are like looking deeply into a cloudless night sky during the new moon, from a high mountain, close to the stars.