Oolite

Oolite, also known as ool stones in the lands around the Sea of Fallen Stars, was a variety of quartz which occurred in tiny egg-shaped spherules.

Description
These ornamental stones were usually solid brown in color and were very similar to algae. Individual oolite spherules were about $1/16$ in (1–2 mm) or less, which was too small to be cut. The aggregate stone was usually polished to bring out the color and mounted in silver jewelry (particularly tiaras or pectorals), or used as eyes in sculpted figurines or to create patterns on chased metals. A typical stone had a base value of 10 gp.

Powers
Powdered ool stones were a prized ingredient when casting spells that purified or neutralized, and in making the magic ink for scribing those same spells.