. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. QUARTZ (MOCHA-STONE—MOSS-AGATE) 507 brown, red or black dendritic markings resembling trees and j)lants. These have been formed by the percolation of a solution containing iron or manganese through the fine cracks of the stone, and the subsequent deposition of the colouring matter originally held in solution. The brown and red marking are caused by
. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. QUARTZ (MOCHA-STONE—MOSS-AGATE) 507 brown, red or black dendritic markings resembling trees and j)lants. These have been formed by the percolation of a solution containing iron or manganese through the fine cracks of the stone, and the subsequent deposition of the colouring matter originally held in solution. The brown and red marking are caused by oxides of iron, and the black by oxide of manganese. The fact that such tree-like markings are formed when a liquid travels in such a confined space can be easily shown experimentally by means of a coloured solution between two plates of glass. The dentritic markings of mocha-stone lie to a large extent in the same plane, and in cutting this stone the lapidary aims at displaying the marking with a coating of chalcedony of only just sufficient thickness to preserve it from injury. The surface of cut stones is either plane or slightly convex, and their outline may be round or oval. A mocha-stone suitable for mounting as a brooch -pia. 89. Mocha-stone, is represented in its actual size in Fig. 89. Certain rare mocha- stones in which the white or grey chalcedony shows, besides dendritic markings, the red dots characteristic of St. Stephen''s stone are specially beautiful. Dendritic agates of this description are said to have come originally from the neighbourhood of Mocha in Arabia, a seaport at the entrance of the Red Sea; hence the name " ; In later times it has been obtained principally from India, where it occurs in the Deccan traps (see under agate). Fine stones are met with as pebbles in the Jumna river, and the mineral also occurs in large amount north of Rajkot and the Kathiawar peninsula, and in the bed of the Majam river in the same district. Here
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