S60 



NEW VARIETY OF CARBONATE OF LIME. 



Only two laws 

 to add to tliose 

 before known. 



Trill exaedi-al 

 carbonate of 

 lime. 



Prisrnatte hy- 

 aline quartz. 



New rariety of 

 carbonate of 

 liise. 



Its figure, 



In the applications I have made of the theory to these 

 varieties I have found but two laws to add to the twenty- 

 one I had mentioned in my treatise as those, of which I had 

 then recognised the existence. The first determines in part 

 the structure of a variety, which I have called trihexae^ 

 dral carbonate of lime, because its figure is that of a six- 

 sided prism, terminated by right pyramids of the same num^ 

 ber of faces. Three of these faces are parallel to those of 

 the primitive rhomboid, and the other three, which have 

 the same inclination, result from a decrement by two rows 

 in height on the inferior angles e, Fig. 2, Plate X, of the 

 same rhomboid, so that if this law attained its limits, the 

 secondary form resulting from it would be similar to the 

 nucleus. This structure is likewise that of the prismatic 

 hyaline quartz, which I have described in my Treatise on 

 ISIineralogy. vol. ii, p. 411 ; but in the quartz crystals the 

 inclination of the terminal faces to the adjacent sides ia 

 141'= 40', while in the carbonate of lime it is only 135^ ; 

 which arises from the dift'erence that exists between the pri- 

 mitive forms themselves. I am indebted to Mr. Hericart- 

 Thuri, mine-engineer, for the knowledge of this interest- 

 ing variety, a specimen of which he has presented to me. 



Tiie second law relates to the variety, that forms the 

 subject of this article. The crystals, that have enabled me 

 to determine it, were sent me from Clermont-Fcrrant by 

 Mr. Augustus Mabru, whose useful researches in the de- 

 partment of Puy-de-D6me, as well as those of his worthy 

 friend Mr. dc Laizer, aftord new proofs of the mineralogi- 

 cal treasures contained in that country. I avail myself of 

 this opportunity, to render them both a public testimony of 

 my gratitude for their eagerness to impart to me the fruits 

 •f their discoveries, particularly with respect to the species 

 sulphate of barytes, of which they have sent me a consi- 

 derable number of varieties hitherto unknown; and this 

 pleasure has been greatly enhanced, as the symbols repre- 

 senting the laws of their structure, given in the letters ac- 

 companying them, generally announce observers equally 

 fittentive and enlightened. 



Ft'g. 3 represents fhe variety in question. Mr. Mabru 

 liad very justly reujarked, that it exhibited a rhomboid with 



equa^ 



