1851.] On a Series of Calderite Rocks. 209 



The weathered surface resembles that of some kinds of hornblende 

 rock. 



No. 9. — A. fine-grained resinous rock ; like powdered black rosin 

 agglomerated in a mass. 



No. 10. — Is the specimen which I have described as the type of the 

 mineral in my former paper upon it ; which for the sake of connexion 

 I copy here. 



" This rock can be in no way so well described as by saying, at 

 once, that while on the weathered surfaces it resembles a common 

 massive ore of iron, its appearance on the fresh fracture is exactly 

 that of black rosin. When examined by the magnifier it is seen to 

 have a golden resinous (which is yellow quartz) coating, in thin 

 laminae, especially on some of the fractures. On others it has small 

 specks which are seen by the magnifier to be minute cavities full of a 

 yellow powder. 



" The fracture is difficult to describe, being in some places hackly, 

 in others tending to small conchoidal, and in some instances breaking 

 on a large scale into an obliquely rhomboidal cavity, as if the rock 

 would cleave naturally into oblique rhomboidal prisms, or contained 

 crystals of that shape. The most perfect cavity I could measure, for 

 I could not obtain a good solid angle, was one of 1 24°, giving therefore 

 56° for the acute angle of the rhomboidal crystal. 



" The splinters are often nearly laminar and sometimes highly trans- 

 lucent, like dark brown rosin. When held to the light these are seen 

 to contain, here and there, fragments of bright white quartz. 



"The streak is ash-coloured, and obtained only with the file, or on 

 a salient edge by the knife. It is brittle, and easily fractured with a 

 moderate blow. The powder is fawn-coloured. When breathed upon 

 it gives a metallic odour. The latter portions are tough and difficult 

 to pulverise, requiring repeated sifting and hard pounding. 



" Its hardness is 7.8. The specific gravity 3.65. 



" The solid mineral does not alter by digestion in acids, and even 

 in nitro-hydrochloric acid ; hydrochloric acid dissolves a little iron, 

 but in very small proportion (probably from dust) even from extremely 

 thin pieces.'' 



No. 11. — A lighter coloured variety of No. 10; having on some 

 parts, and in a good light, the appearance of impure yellow rosin. 



2 K 



