DESCRIPTION OF THE DICHROIT. Q^^ 



to varieties of known substances, and particularly to the 

 blue tourmaline. 



Before [ proceed to describe the dichroit, I ought to 

 observe, that it is not mentioned in Delametherie's Theory 

 of the Earth, Haiiy's Treatise on Mineralogy, Patrin's 

 work, Brongniart's, the Abstract of Haiiy's Method by- 

 Lucas, or any other work yet published in France. 



Hitherto the dichroit has been found only in amorphous How found, 

 or crystallized grains, sometimes collected in small masses, 

 not four inches in diameter. 



Its essential character is its being divisible parallel to Essential cha» 

 the faces of a regular hexaedral prism, and capable of sub- racter. 

 division by longitudinal sections perpendicular to the lateral 

 faces. 



Its specific gravity is 2-56. Physical cha* 



It scratches glass strongly, quartz feebly ; and is easily r^cters. 

 broken. 



Its fracture is vitreous, tolerably shining, and frequently 

 giving very evident indications of scales. 



Its fragments are irregular with sharp edges. 



Its powder feels very rough. 



The lustre of the external surface commonly dull. 



The tran^lucid crystals exhibit a particular phenomenon, 

 which may be called that of double colour by refraction. 



Its primitive form is a regular hexaedral prism. Geometrical 



Its integrant particle is a triangular prism, the bases of characters. 

 which are scalene rectangles. 



It is not acted upon by acids. Chemical cha- 



Before the blowpipe it fuses into a very light greenish '^acters, 

 gray enamel. A similar result is obtained either with borax 

 or carbonate of soda. 



The dichroit is distinguishable, I, from the emerald, be- Distinguishing 

 cause the specific graA(*ity of the latter is greater in the pro- characters. 

 portion of 10 to 9; its integrant particle is an equilateral 

 triangular prism; and it fuses more difficultly : 2, from the 

 tourmaline, in qot becoming electrical by heat, and in be- 

 ing less hard, and less heavy: 3, from the corundum, in 

 the latter being infusible, and affecting a rhomboidal pri- 

 ' mitive form : 4, from the dipyre, or leucolite, because the 

 latter fuses with ebullitipo, and its powder is more phospho- 

 rescent : 



