558 Intelligence and Miscellaneous Articles. 



phacolite, according to Breithaupt, is P on P, 94°, that of chabasite 

 P on P, 94° 24'. Phillips makes the last 94° 46'. The analyses of 

 Anderson and Rammelsberg would seem at first to show a marked 

 difference in their composition, a difference which is also shown by 

 the different analyses of common chabasite, resulting in varieties 

 having different formularic expressions. For example, acadiolite 

 contains three per cent, more of silicic acid than common chabasite, 

 and is a tersilicate of lime and the other isomorphous bases, instead 

 of a bisilicate of the same bases. The mineralogical formula of 

 acadiolite is 3A1 Si 2 + (Cal, N, K,) Si 3 + 6 Aq, while that of chaba- 

 site is 3AlSi 2 + (Cal, N, K,) Si 2 +6 Aq. Rammelsberg is inclined 

 to regard phacolite as a mixture of acadiolite and scolecite (lime 

 mesotype), the latter containing an additional atom of water*. By 

 uniting the atoms of both, he thus states the chemical formula for 

 phacolite : 2RO SiO 3 + 2A1 2 3 3Si 3 O 3 + 10HO. As the analyses 

 stand (compare Berzelius's and Thomson's with the two just re- 

 ferred to), phacolite differs from chabasite in containing three per 

 cent, less of silicic acid, and three atoms less of water. Now it is 

 obvious that these differences are insufficient to authorize a separa- 

 tion of the two minerals, unless there be a want of agreement in cry- 

 stallographical and other characters, greater than that as yet pointed 

 out. An equally valid reason could be urged for the separation of 

 acadiolite from chabasite, on the ground of a difference in their com- 

 position, had not the examinations of Prof. Gr. Rose proved an exact 

 agreement in the angles of their primary crystals. So, also, of levyne 

 and gmelinite, which are now admitted to be only varieties of cha- 

 basite, their occurring forms all being secondaries to the same pri- 

 mary rhombohedron. The evidence of the identity of any two 

 minerals is best shown by the incipient or intermediate passages of 

 one into the other, in the same specimen. I am not aware that, in 

 the case of the Irish or Bohemian phacolite, such evidence has been 

 adduced ; no tendency of the sort is shown in the specimens I have 

 examined from those countries. Now one of my specimens from 

 New York has the distinct form of chabasite (the perfect rhombo- 

 hedron) and of phacolite (perfect double six-sided pyramids). The 

 first form, however, is rare ; the incipient replacements are also 

 shown ; but these crystals have not the full perfection of waxy lustre 

 reflected by the ultimate form of phacolite, — a singular effect, attri- 

 butable, probably, to the nature of the solvent in which the molecules 

 were suspended. 



Approach of twin-crystals to the Phacolite form. 



These, as they are sometimes presented, would, unless carefully 

 examined, be mistaken for the true form of phacolite. The most 

 perfect specimens I have seen are from Nova Scotia. They consist 

 of two rhombohedrons united in the usual manner, each crystal 

 turned half round, but having their superior edges and lateral angles 



* See First Suppl. to his Handworterbuch, p. 112. It was on these 

 grounds that Hoffmann proposed to separate acadiolite, as well as the Gus- 

 tafsberg variety, from chabasite. — PoggendorfF's /lnnalen, xxv. 495. 



