116 



arc developed in the Lizard District of Cornwall, fl) in Anglesea, ( ' 2) in 

 Ayrshire l3 ' and Aberdeenshire. (4 ' 



With regard to field relations, he believes that in the Lizard and 

 in Ayrshire the appearances can only be explained on the assumption that 

 the mother-rock of the serpentine was intrusive. In the other cases the 

 field relations are not so clear; but as nothing- was seen to negative the 

 view that the original rock was igneous and as the serpentines from all the 

 above localities resemble each other in their petrographical characters, he 

 concludes that they are all of similar origin. 



Typical serpentine is a compact rock with a splintery or, in some cases, 

 conchoidal fracture. It is readily scratched with a knife (hardness about 

 '} or 4), and possesses a specific gravity of 2'5 or 2'6. It varies extremely 

 in colour and, as it takes a good polish, has been extensively used for 

 the purpose of making small ornaments. The brittleness of the rock and 

 the difficulty of obtaining large blocks free from joints prevents its general 

 use for the larger ornamental purposes. 



The prevailing tints of the ornamental serpentines are yellowish green, 

 pale green, deep green, brownish red and blood red. Irregular blotches or 

 anastomosing veins of one colour often occur in a groundmass of another 

 colour. Thus, some of the most beautiful varieties are due to blotches and 

 veins of a blood red variety of serpentine in an olive-green groundmass. 

 Veins of chrysotile and white steatite and porphyritic crystals of bastite 

 frequently occur. In addition to the above varieties, all of which are more 

 or less used for ornamental purposes, we find largely developed in the Lizard 

 peninsula and occurring also in Ayrshire, a black variety with conspicuous glisten- 

 ing crystals of bastite. In the former locality also occur dark banded serpentines 

 with minute glistening crystals of a pale coloured hornblende (grammatite). 

 This latter variety also occasionally contains large porphyritic crystals of 

 bastite. 



As a rule serpentine is dull and opaque ; sometimes, however, it 

 is translucent. Translucent varieties suitable for the more delicate 

 ornamental purposes are termed noble serpentine. The only British locality 

 in which noble serpentine has been recorded, so far as the present writer 

 is aware, is Hills wickn ess in Shetland. 15 ' 



White steatite, a substance which differs from serpentine in containing 

 more silica and less water or, in more precise chemical language, in being a 

 bisilicate instead of a uni-silicate, often occurs in association with serpentine. 

 Sometimes, as already mentioned, it forms veins in the serpentine, and at 

 other times angular fragments of normal serpentine lie embedded in a white 

 steatitic groundmass. 



To describe all the macroscopic varieties of serpentine would be an 

 endless and unprofitable task. They are doubtless due partly to variations 



(1) Q.J.G.S., Vol. XXXIIL, (1877), p. 884. 



(2) Q.J.G.S., Vol. XXXVII. , (1881), p. 40. 



(3) Q.J.G.S., Vol. XXXIV., (1878), p. 769. 

 (_4) G.M., Decade III., Vol. II., (188-5), p. 439. 



(5) Dr. HKIDLK. Trans. Roy. Soc., Ediii , Vol. XXVIIL, p. 239. 



