This listing is for the smaller nut set with  iolite.

Iolite is the gem variety of the mineral cordierite. The name "iolite" comes from the Greek word for "violet." Iolite is known for its violet-blue to grayish-blue color as well as pleochroism: it can show different colors when viewed from different angles. Historically, iolite was called the "Viking's Compass" because Norse explorers
were said to used the stone to navigate by the sun on cloudy days. Sounds like something to learn more about to me.

Little sterling nut set with iolite, 5.5mm diameter opening, 10.5ish mm diameter.