56 M. Rose on Felspar, [Jan. 



Third Species. — Labrador. 



This substance is very seldom met in regular crystals. There 

 is only one specimen in the collection of minerals at the Univer- 

 sity of Berlin ; and although it is possible to determine the form 

 of it, which shows great analogy with felspar, the angles can- 

 not be measured. The modifications appear to be the same as 

 those of felspar. It cleaves easily in two directions, in one of 

 which the face obtained by cleavage is perfectly brilliant ; the 

 difference between the degree of brilliancy ©f these two cleav- 

 ages denotes a difference between labrador and felspar. 

 Moreover those two cleavages are not obviously at right angles 

 to each other. I have found their inclination to be 93^° and 864°. 

 I could not measure more exactly the incidence of these two 

 cleavages on account of the dulness of one of them. There is a 

 third cleavage still more imperfect, and which corresponds with 

 one of anorthite, but not with any of albite. 



Thin lamina* of labrador are of a whitish-grey; the fine reflec- 

 tion of light which distinguishes this substance is given by one 

 of the cleavages. 



The specific gravity of a fragment of labrador (from Labrador, 

 in America) weighing 10*576 grs. was found, using water at the 

 temperature of 18° R. = 2-7025. 



The specific gravity of a fragment weighing 12-068 gr. from 

 the same locality, using water at the temperature of 17|° R. = 

 2-695. 



According to Brisson, = 2-692. 



According to Klaproth, = 2-690. 



Specific gravity of the labrador from Ingremanie, according 

 to Klaproth, = 2-750. 



One hundred parts of labrador from Labrador, and an equal 

 quantity of labrador from Ingremanie, contain, according to 

 Klaproth, 



Labrador from Labrador. Labrador from Ingremanie. 



Silex 55-75 55-00 



Alumina 26-50 24-00 



Lime 11-00 10-25 



Oxide of iron. 1-25 5-25 



Soda 4-00 3-50 



Water 0-fi0 0-50 



99-00 98-50 



Berzelius has calculated from these analyses the mineralogical 

 formula 



N S- 1 + 3 C S 3 + 12 A S. 



Observations. — Labrador and felspar present similar charac- 

 ters with the blowpipe ; and for this reason Berzelius was induced 

 to suppose that the mineral analyzed by Klaproth, under the 

 name of labrador, was iridescent pareathine, with which it has 



