'25 



TAB. CCCXVIL 



CALX carbonata. 

 Carbonate of Lime. 



Div. l. Crystallized,, . 



IVIineralogical Nomenclators have given titles to crystals 

 under various circumstances, such as Mackles or Twins ; 

 and I have exhibited crystals upon crystals which might 

 have some corresponding or expressive term. The present 

 is peculiar as to its structure, and is as it were seamed, and 

 although now perhaps newly noticed, is certainly of as much 

 consequence as many others, especially as it will furnish 

 two very instructive and useful examples in Crystallography, 

 which captivates the fancy so many ways. Here is a 

 half of the Metastatic* Crystal covered on the three obtuse 

 angles of the pyramids by a thick coat spreading on either 

 side, till it meets nearly on the acute angles, forming upon 

 them a plane with a line or seam in the middle of it, which 

 makes the modification more conspicuous, at the same 

 time it is helped by a difference in the inner crystal, which 

 is somewhat more opaque and whiter than the outer cover- 

 ing; and in many lights we see the white reflection between 

 the two surfaces. The three varied quadrangular faces are 

 belonging to the common prism of this substance; those with 

 the seams form somewhat rounding curved truncations to 



* Metastatic means the transposition that happens of the angles of the 

 pucleus on to the secondary crystal. 



