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 " mocha-stone." 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 are 

 found blocks of spherical, botryoidal, or amygdaloidal form, weighing as much as 40 pounds, 

 as well as rounded pebbles. Fine material suitable for cutting occurs also at various places 

 in North America ; for example, at Central City in the Rockv Mountains. 



The most valuable mocha-stones are those in which the dendritic markings closely 

 resemble the outlines of trees and plants ; stones in which the markings take the form of 

 irregular black and brown patches arc worth but little. Very good imitations of mocha- 

 stone are now produced, an Oberstein agate-dealer having succeeded in producing permanent 

 markings of a kind similar to those of mocha-stone on the surface of cut chalcedony. 

 These artificial productions are far more beautiful than the naturally occurring mocha- 

 stone, but otherwise are difficult to distinguish from these. Both the natural and the 

 artificial stones were at one time much used, and commanded a high price, but this is not 

 the case at the present time. 



Moss -agate is characterised by the presence of green enclosures, such as are found 

 in many specimens of rock-crystal. These enclosures usually take the form of long hairs 

 and fibres much intertwined, and have the general effect of a piece of moss ; hence the 

 term moss-agate. The stone is common in the volcanic rocks (trap) of western India, 

 occurring in places with mocha-stone. It fills irregular veins in the decomposed trap 

 at Rajkot, among other places, where blocks ranging in weight from ^ to 30 pounds 

 are obtained. It occurs also as pebbles in many Indian rivers, for example, in the 

 Narbada, Jumna, and Godavari. A supply of natural green and of artificial yellow and 

 red moss-agates has been obtained for some time from China, and these stones have largely 

 replaced others on the market. Fine moss-agates occur in considerable numbers in the 

 States of Utah, Wyoming, Colorado, and Montana, in North America. 



EnhydrOS are stones which are more curious than beautiful, and are used but little 

 as gems. They are flat, oval, and hollow nodules of strongly translucent, almost colourless 

 chalcedony, partly filled with water. The water thus imprisoned can be distinctly seen 



