Amethyst geode with a wide rock crystal rim

A Brazilian amethyst geode with an unusually wide rock crystal rim. The bright rock crystal border clearly defines the violet amethyst core.

Such rock crystal rims are formed by zoned mineralization. In the first growth phase, pure quartz crystallized without iron substitution. Only in later phases did iron-containing solutions appear and color the main amethyst body violet.

A wide rock crystal rim is a collectible detail property. It makes the growth history of the geode legible and contrasts clearly with the violet core.

Brazilian deposits in Rio Grande do Sul supply this material. The constellation of a rock crystal rim plus an amethyst core is a double collector's feature.