114 



Mr. Brooke on Baryto-Calcite. 



[Aug. 



Fig. 1, represents the rain gauge in perspective. 



Fig. 2, is a vertical section. 



G the body of the gauge, F its funnel, L the lid or cover, 

 v the valve, hinged to the lower orifice of the funnel, s the spring 

 to close the valve, w a wire to conduct the drainings of the funnel 

 into the body of the gauge. 



Article VIII. 



On Baryto-Calcite. By H. J. Brooke, FRS. &c. 



(To the Editors of the Annals of Philosophy.) 



GENTLEMEN, July 15, 1824. 



Mr. Broughton, before he left. London, favoured me with 

 specimens of a mineral from Cumberland which had been con- 

 sidered to be carbonate of barytes, but it was very evident that 

 the crystals did not resemble the ordinary figures of carbonate 

 of barytes, and the substance was, therefore, regarded by Mr. 

 Broughton as something new. 



The external surface of the specimens is coated with sulphate 

 of barytes ; but the internal mass frequently 

 contains cavities which are lined, and / 



nearly filled with crystals. The primary / 

 form of these is an oblique rhombic prion, as f\^ j 

 shown in the annexed figure, the cleavage 

 being parallel to the planes P, M, and M'. 



P on M, orM' 102° 54' 



Pona 147 34 



P on h 106 8 



MonM' 106 54 



M on h 143 27 



All the crystals I have seen are modified on some of the edges 

 and angles, and are lengthened in the direction of the edges of 

 the modifying planes, presenting the character of prisms termi- 

 nated by the bright, planes Y, a, M, and h, of the figure. The 

 modifying planes are, however, so numerous, irregular and dull 

 in my specimens, that I have not obtained sufficiently good or 

 corresponding measurements to enable me to ascertain their 

 character, anti they are, therefore, omitted in the drawing. 



The mineral is translucent with a slight tinge of a yellowish- 

 brown colour. 



Its lustre rather more waxy than carbonate of barytes. 



Its hardness is between that of carbonate and filiate of lime. 



Its specific gravity, as ascertained by Mr. Children, is 3*66. 



The name baryto-calcite has been given from its chemical 

 composition, as ascertained by Mr. Children. 



» The mean specific gravity of carbonate of barytes and carbonate of lime is 3-5. — C 



