a Nexo Mineral Species. 265 



but transmits light when reduced to a considerable degree of 

 thinness. It often contains small spherical groupes of fila- 

 mentous crystals, intensely white, which, if they are Gmelin- 

 ite, which is not probable, must have lost their water of crys- 

 tallization. 



The specific gravity of the flesh-coloured Gmelinite, from 

 the Vicentine, is 2.05, and its hardness about 4.5, scratching 

 glass with some difficulty. The crystallized variety from 

 Glenarm appears to have a less degree of hardness. 



The optical structure of the Gmelinite differs entirely from 

 that of the Analcime, or the Chabasie, both of which are com- 

 posite minerals, the individuals of which they are composed 

 having never yet been found in nature. The double refraction 

 of Gmelinite exceeds that of Analcime and Chabasie, and may 

 be distinctly seen through the two opposite faces of the pyra- 

 mid by immersing it in water, which gives a great degree of 

 transparency to the Glenarm crystals. The double refrac- 

 tion is negative in relation to the axis of prism, which is the 

 axis of double refraction. 



The flesh-coloured masses from the Vicentine are also sim- 

 ple substances, which, though rendered imperfectly transpar- 

 ent by flaws and disseminated matter, give distinctly the colours 

 of polarised light. Their index of ordinary refraction is about 

 1.474, less than that of almond oil. By immersing the sum- 

 mit of one of the Glenarm crystals in a parallelopiped of 

 almond oil, I was enabled, without detaching the crystal 

 from its matrix, to ascertain that its refractive power was 

 also inferior to that of almond oil, and in the same degree as 

 the flesh-coloured masses. As the refractive power, both of 

 Analcime and Chabasie exceed considerably that of almond oil, 

 this simple experiment, which requires no other skill than that 

 of looking through the crystal, establishes the identity of the 

 minerals from Glenarm and the Vicentine, and fixes them 

 as a new mineral species different from Analcime and Chabasie. 



The chemical characters of Gmelinite are not less distinc- 

 tive and interesting than its optical ones. When we hold a 

 fragment of the Vicentine crystals near the flame of the candle, 

 and supported in a loop of platinum wire, small portions gra- 

 dually raise themselves, and after standing on their ends as if 

 they were under the influence of electricity, they are propelled 



