58 Mr. Rose on Felspar, Albite, Labrador, #c. [Jan. 



Pone 137° 22' 



PonT 110 57 



Ponj/ 125 38 



Mono' 115 20 



Monu' 122 45 



M'onm 116 12 



Pone' 91 56 



M on v' 141 54 



Pona/ 98 37 



M'onw' 141 22 



Plane Angles of the Primitive Form. 



Those of plane P 121° 33' and 58° 27' 

 M 116 15 63 45 



T 106 42 73 18 



Anorthite, as well as albite, although not quite so frequently, 

 presents also hemitrope crystals, I have not given drawings of 

 them, because they are formed exactly according to the same 

 laws. This substance can be cleaved parallel to the planes P 

 and M with equal facility. I have not been able to obtain a 

 cleavage parallel to the plane T, and I have chosen it for one of 

 the primitive planes in preference to the plane /, because it is 

 generally much more brilliant. The fracture in other directions 

 is conchoidal. The lustre of the cleavages is pearly, and that 

 of the conchoidal fracture vitreous. 



Anorthite is found sometimes crystallized in small masses. 

 The crystals are perfectly clear and transparent, but very small. 



The specific gravity of several fragments weighing 1*463 gr. 

 bv using water at the temperature of 14° R. has been found 

 equal to 2-763. 



That of small crystals weighing 0*316 gr. mixed with a small 

 quantity of pyroxene, by using water at 17° R. was found equal 

 to 2*656. 



Concentrated hydrochloric acid entirely decomposes anorthite. 

 I have found 100 parts of anorthite, the specimens of which, as 

 well as those of albite, I had obtained through the kindness of 

 Mr. Weiss, from the collection of minerals in the University of 

 Berlin, composed of 



Silex 44*49 which contains oxygen 22*38 ""111 



Alumina 34*46 16*096^ , R Qofi Q 



Oxide of iron 0*74 0*23 j ltr,i ~ b > 6 



Lime 15*68 4*40 2 



Magnesia 5*26 2*04 J 1 



Another analysis in which 1 had only 0*6 gr. to examine gave, 

 however, similar results, and consequently the mineralogical 

 formula is 



MS+2CS+8AS 



