LHERZOLITE. 287 



biotite. Serpentites derived from this rock are found in Elba, and at 

 Monte Ferrato in Tuscany. In Elba the rock is very rich in olivine, 

 while in the Tuscan localities it is subordinate to the diallage. 



Eulysite is a similar rock, and may be described as an olivine- 

 iliallage with accessory garnet. The Bohemian garnets are derived 

 from this rock. It is sometimes converted into serpentine. 



The garnet-olivine rock of Mohsdorf in Saxony is not to be 

 separated as a distinct rock, though the garnet is sometimes wanting, 

 and then the rock is a compound of olivine and diallage. 



Olivine-Enstatite consists of olivine, rhombic pyroxene, enstatite, 

 bronzite or hypersthene, and always contains magnetite or chromite. 

 It is seen in Russdorf in Saxony. A hornblendic variety occurs at 

 Crube Varallo in the Monte Eosa district, and a variety rich in garnet 

 is found near Heiersdorf in Saxony, where the rock also contains 

 zircon. Several examples of bronzite serpentines are iue to the 

 decomposition of olivine-enstatite. 



Lherzolite, according to Professor Bonney, is a crystalline aggre- 

 gate of olivine, enstatite, and diopside with some picotite. Its tex- 

 ture is granular, and the grain may be either fine or coarse. It occurs 

 around the small tarn of Lherz, in the Eastern Pyrenees, in the depart- 

 ment of Arriege. It is a tough rock of olive-green colour, with olivine 

 for the predominant mineral ; it contains emerald-green spots of 

 diopside, dull waxy green spots of serpentine, resinous-looking grains 

 of enstatite, and minute black grains of picotite. The exterior weathers 

 to a bright yellowish or a rusty brown. There are seven exposures 

 in the district, all intrusive in the Lias. Under the microscope olivine 

 is seen in roundish grains, showing between crossed nicols, colours vary- 

 ing from greenish yellow to yellowish green, and from a bright pink 

 to a purple pink, The enstatite is in irregular or long grains ; it is 

 colourless in ordinary light, but in polarised light varies from pale 

 yellow or grey to some, tint of blue. The diopside rarely occurs in 

 distinct crystals. In polarised light the colours are less clear than 

 those of olivine, and usually vary from rich yellowish brown to puce. 

 Picotite may occur in groups of grains or films. Its colour is olive 

 green to umber-brown, and is dark between crossed nicols. The 

 serpentine, which appears to result from the decomposition of the 

 olivine, shows between crossed nicols a pale golden tint. 1 



The Lherzolite at Konradsreuth in the Fichtelgebirge, according 

 to Gunibel, 2 is accompanied by an altered olivine slate now converted 

 into talc slate and actinolite schist. It is associated with eklogite 

 and diorite, and with them is contained in syenitic gneiss. The 

 Lherzolite here, too, is converted into serpentine, and it is probable 

 that many serpentines will prove to have been originally a rock of 

 this kind, especially the serpentines of the Vosges, the Lizard, and 

 the department of Yar. 



Dunite, originally described from New Zealand, consists of olivine 

 and chromic iron. In the south of Spain, at Serrania de Honda, the 



1 Bonney "On the Lherzolite of the Arriege," Geol. Mag., Feb. 1877. 



2 Gumbel, Fichtelgebirge, 1879. 



