John Parkinson — Gahhro of Pegli, N. Italy. 295 



glaucophane in tlie body of the diallage, an entire replacement 

 by the former mineral is obtained ; the characteristic diallage 

 striation remaining even when scarcely any trace of the original 

 mineral can be seen. The formation of closely massed flakes of 

 glaucophane in cracks which crushing has caused in the diallage 

 is also common. Professor Kot5 has described many similar cases 

 in the paper previously mentioned. The diallage passes directly 

 into glaucophane. The dark, rather yellowish brown of the former 

 mineral is lost in great measure with some abruptness, and the 

 characters of the glaucophane assumed. Frequently it is crowded 

 with granular enclosures which are most probabl}'' an excretion or 

 residuum from the manufacture of the secondary mineral. They 

 occur abundantly in those flakes which can be certainly demonstrated 

 to have arisen from the diallage, rather than in those films and scales 

 whose origin from tlie pyroxenic mineral cannot be so readily 

 determined. They are entirely absent from the diallage in its 

 freshest condition, and wlien the glaucophane is traversed by cracks 

 now filled by secondary minerals, the granular mineral is absent ; 

 from which may be inferred that it does not form where the facilities 

 for the removal of material are easy. The habit and high polariza- 

 tion tints strongly reciU epiilote, and it is most probable that the 

 major part of the lime has been used up in this way. The rather 

 high iron percentage of glaucophane makes it probable that most 

 of this constituent present in the diallage would be used in the 

 formation of the former mineral, and the presence of some quantity 

 of zoisite with the epidote may be inferred therefrom. In some 

 sections the glaucophane appears as a closely packed mass of flakes, 

 straight or slightly wavy ; which are arranged in groups or bundles 

 with a slight tendency to a radial disposition, and not unmixed with 

 actinolite or a kindred mineral. In one or two cases this glauco- 

 phane becomes minutely fibrous, and is then probably the same as 

 the mineral Koto has termed crocidolite, and which he believes to 

 result from an alteration of the glaucophane. Here and there, but 

 not commonly, in the Pegli gabbro the pleochroism is different to 

 that of either normal or dark glaucophane, and is characterized by 

 a blue-green or sea-green tint. The variety is platy or fibrous, the 

 former paler in colour. The occurrence of the nearly allied species 

 crocidolite on or near the north-western coast of Italy has beau 

 recorded by M. Lacroix' from Cape Argentario, near Orbetello, 

 and from the island of Gorgona, to the west and a little to the 

 south of Leghorn. That from the first locality is formed from 

 diallage. M. Lacroix states that in his opinion many secondary blue 

 hornblendes, described as glaucophane, are really crocidolite. Such 

 an instance may, he thinks, be found in the blue amphibole partly 

 replacing pyroxene, which has been described as glaucophane from 

 a rock occurring in South Central Spain.- 



The same author^ has noticed a variety of glaucophane distinguished 



1 Biill. de la Soc. Min. de Fr., vol. xiii (1890), p. 10. 

 - Comp. Rend., vol. cii (1886), p. 640. 

 3 Min. de la Fr., vol. i, p. 700. 



