252 Dr. Hecklle and Mr. It. P. Greg on British Pectolites. 



CaO is to the NaO in the proportion of 4 to 1), and rejecting 

 the HO, make the mineral come under the hornblende formula, 

 viz. — 



4RO, 3Si0 3 , 



RO standing for CaO, MgO, FeO 3 , Al 2 O 3 , NaO. 



We have, in calculating the formula from our analyses, chosen 

 the crystals from Ratho as in all probability the purest : — 



Oxygen. Atoms. 



SiO 3 , 52-580 = 26-209 = 11-03 = 11 11 



CaO, 35-206 = 10016= 4-25 = 4 12 



NaO, 9-258= 2-376= 1=1 3 



HO, 2-800= 2-489= 1-05= 1 3 



giving the formula — 



3(NaO, Si0 3 ) + 4(3CaO, 2Si0 3 ) + 3HO; 



the calculated per-centages of which are, — 



Silica 11 atoms = 508409 = 52-574 

 Lime 12 atoms = 337956 = 34-947 

 Soda 3 atoms = 93629 = 9-683 

 Water 3 atoms = 27039 = 2-796 



937043 100-000 



This, it will be allowed, is a still closer approximation than 

 the per-centages of the hornblendic formula, and this also is the 

 formula given by Berzelius. 



Now this formula points, not to hornblende, but to augite, for 

 it will be seen that it is the same as that of table spar, 3CaO, 

 2 SiO 3 ; only neutral silicate of soda replaces silicate of lime, and 

 table spar is an augite, the formula of which is 3RO, 2 SiO 3 

 (where RO may stand for CaO, MgO, NaO, Fe 2 O 3 , Al 2 O 3 , &c.) ; 

 for if it is allowable to disregard for the time being the HO, in 

 order to bring the mineral among the hornblendes, the same 

 course cannot be objected to, to bring it among the augites. 



The crystalline form of pectolite, as we have ascertained from 

 the Ratho crystals, is the same as Wollastonite, with which it is 

 therefore isomorphous. The accompanying figure represents the 



Cleavage highly perfect, parallel to c and u. Twin face c. The 

 face y coming in the zone z, e, (?/), x of Brooke and Miller, 

 appears to be hemihedral in the Ratho crystals, and is a plane 



