67 



Now, if tho phosphoric acid in Ledererite is united with lime as an 

 accidental mixture, 2^- per cent, of the lime should he taken from 

 the 11-48 per cent, found in the mineral : this brings the proportion 

 down nearly to that obtained by Connell. Mr Hayes was not able 

 to determine the weight of the water with accuracy, owing to the 

 small quantity of the mineral operated upon. As the loss (1-44 

 per cent.) was mostly water, we may suppose, with Rammelsberg, 

 that Ledererite is Gmelinite containing \ (| ?) its quantity of water. 

 The chemical formula for Gmelinite and Chabasite is thus :■— 



(Ca, Na, k3) Si^ + 3 Al Si^ + 18 H.* 



Excepting the absence of strise, and the shorter dimensions of the 

 prismatic planes of its crystals, the Irish Gmelinite precisely re- 

 sembles Ledererite ; their hardness, lustre, colour, and blowpipe 

 characters, are the same. The appearance of hexahedral cleavage, 

 on which Dr Jackson originally founded the chief claim of the latter 

 to the character of a new species, was only imperfectly produced by 

 heating the crystals, and not by ordinary mechanical cleavage. This 

 could not be effected, the mineral breaking, in all directions, with a 

 vitreous fracture. Dr Jackson agrees with me, that it can no longer 

 be retained as a distinct species. 



While preparing my edition of Phillips's Mineralogy, I requested 

 Mr Hayes and Dr Jackson to make several analyses for me with par- 

 ticular reference to that work. As some of these have not appeared 

 in any other form, I wish now to make a permanent record of them, 

 in order that they may be seen where they might not otherwise reach, 

 the first are of the Nova Scotia Chabasite (Acadiolite), which Hoff- 

 mann has distinguished from common Chabasite, by its containing 3 

 per cent, more silica, and for which Rammelsberg has given a for- 

 mula differing somewhat from that of Chabasite. (See first part of 

 this article). 



^^ Ilandudrterbuch, i., 160. Hammelsberg unites Chabasite and Gmelinite, 

 the first as soda Chabasite, the last as lime Chabasite. This is in accordance 

 with Tamnau, who has established their identity on crystallographical grounds. 

 Tho close relation of the two mineral* was, however, first shewn by Prof. Mohs. 

 See his Mineralogy, vol. ii., p. 105. 



