178 A Book of Precious Stones
States are cut and mounted; in the tourist the Western jeweller and curio-dealer finds for these American moss agates a good customer.
Mocha stone ("tree stone" or dendritic agate) is a white or grey chalcedony showing brown, red, or black dendritic markings resembling trees and plants. These have been formed by the percolation of a solution containing iron or manganese through the fine fissures of the stone, and the subsequent deposition of the colouring matter originally held in solution. The brown and red markings are caused by oxide of iron, and the black by oxide of manganese.
Agate in general is but little used in modern jewelry, but for art objects and interior architectural decoration it is always in demand. For centuries, the centre of the industry of cutting and polishing agate has been Oberstein, Germany; an authentic record shows that this industry has existed there since 1497; the industry has for many years been shared by the neighbouring towrn of Idar. The subject of agate, its origin, mining, treatment, and use in the arts, might worthily supply material for an extensive book.