49 



TAB. CXXVII. 



BARYTES carbonata. 

 Carbonate of Barytes* 



We are obliged to F. Hall, Esq., of Arkendale near Rich- 

 mond, Yorkshire, for the superb specimen from part of which 

 this figure was taken : it is at first sight very interesting, as 

 the crystallization is apparently a most perfect representa- 

 tion of the dodecaedral Quartz, with the two hexaedral 

 pyramids meeting at their mutual base without any inter- 

 mediate prism — a very rare circumstance in Quartz. On 

 further examination we find a modification seemingly pe- 

 culiar to itself, and which has never been recognised in 

 Quartz, or in any other substance before : see the right and 

 left hand figures. It is so new in its nature that an expres- 

 sion is wanted for it, as it is not what may be termed 

 mackled, but may rather be called articulated or jointed. 

 These figures have one or two joints, lengthening the 

 crystal endways without a tendency to continuing at the 

 mutual bases, or filling up the interruption so as to form 

 the plane of the column; the vacancy is just contrary to 

 those of the Carbonate of Lead, which it somewhat re- 

 sembles in the first instance: see tab. 89, 90, 91, and may 

 be of much utility for external discrimination. We have 

 been able by this specimen to determine partly the measure, 

 and compare with Quartz — the incidence of one of the 

 pyramids of Quartz upon the other measuring, according 

 to Haiiy, 103° and some seconds, and we find it in Car- 

 bonate of Barytes to measure above 126°. 



VOL. II. F 



