Jewels

Jewels are inserted in, mainly watches, to reduce friction on the gear train. Until the 20th century, watch jewels were made of ruby, sapphire, aquamarine, garnet, and diamond. I have seen colourless jewels which might be quartz, or low grade (colourless) aquamarine. Pale blue ones are aquamarine or low grade sapphire, and pink ones can be low grade ruby, or possibly garnet. Sapphire and ruby used was usually not of jewellery grade. Diamonds saw limited use, but they show up as balance wheel cap jewels periodically.