Willemite is a rare mineral found in only a few places in the world. Technically, it is zinc orthosilicate. It occurs in crystalline limestone, but rarely forms large crystals and, even more rarely, flat crystals, as found in ceramic glaze.
The very fragile, naturally-occurring flat crystals are quite scarce, and whole crystals are rarely larger than ¼''. As a result whole, flat crystals are highly prized by many collectors.
Within a ceramic glaze, however, these very beautiful crystals can be grown to 2'' or more. And they can form in many interesting shapes.
It is said that in the Congo, where most of the larger crystals are found, it is believed that a Willemite crystal brings happiness and joy to its owner.
Willemite is named after Willem I (1772--1843), king of the Netherlands.