/. Ruskin — On Banded and Brecciated Agates. 531 



orange, and the vertical lines a zone of intense blue. There has 

 evidently been no fracture in this case, any more than between the 

 felspar crystals of common granite. And the — in this instance 

 absolutely accurate — coincidence of direction in the zones of the 

 detached pieces, with their fault-like variation in breadth and relative 

 position, are both of them entirely crystalline phenomena. 



Now we must always remember that in chalcedony and quartz we 

 have two entirely distinct groups of crystalline forces ; one radiant, 

 endeavouring to throw the mass into spherical concretions ; the other 

 rectilinear, endeavouring to reduce it to hexagonal crystals : and 

 that both of these are capable of producing phenomena of relative 

 distortion. 



Also, the groiip of the spheric forces associates itseK delightedly 

 with the spheric forces of hydrous oxide of iron, thus producing 

 endlessly fantastic groups of mixed iron and chalcedony, while the 

 rectilinear forces ally themselves in like manner to those of 

 micaceous iron, bournonite, heavy spar, and calcite, producing 

 tabular groups of crystals which present close analogies to the flat 

 leaves of chalcedonies which, have metallic or earthy laminae for 

 their support ; while the iron-oxide, when it has no longer the power 

 of modifying the shapes of the crystals, sets itself to imitate two 

 other minerals frequently found in them. It mimics the globes of 

 brown, mica so exactly with its own bossy groups of clustered 

 laminae, that only a strong lens, or the knife, will distinguish them, 

 and, in the interior of crystals, throws itself into golden-coloured 

 radiant or circular sheaves which, when within amethyst, are the 

 most beautiful things I know among minerals ; but which it is a 

 matter of great difficulty to distinguish in common quartz from 

 minor forms of rutile. Finally, to crown the complexity of this iron 

 and flint group, the suljjhide of iron, varied beyond all minerals in 

 the phantasies and grotesques which it can build out of its plastic 

 and innumerable cubes, shoots its stellate crystals through the mass 

 of the hydrous oxide, and disputes with it the central position in 

 stalactites of chalcedony. 



But, through all this confusion, one generalization presents itself 

 which is of great value. Whenever iron, whether oxide or sulphide, 

 is associated with stalactitic chalcedony, it is alwaj^s in the centre of 

 the mass ; but when iron, whether oxide or sulphide, is associated 

 with quartz crystals, it is always (if determinately placed at all), 

 either on the outside, or at a slight depth below the surface, under 

 an external coat of clearer crystal. It may be indeterminately 

 placed, in dispersed stars or cubes; but, if ordered at all it is 

 ordered so. Briefly, a crystal of quartz never has a centre of iron, 

 and a crystal of chalcedony never A coat of it.' 



And an important result seems to follow from this. If stalactites 



' Of course I do not vouch for any so "v\nde generalization as this absolutely. If 

 ever one ventures to do such a thing, the next stone one takes up on a dealer's counter 

 is sure to be an exception to the announced law ; but I um confident tliat any 

 mineralogist can fortify the statement from his own experience quite euough to justify 

 our reasoning upon it. 



