420 Reflections on some Mineralogical Systems. 



mul® is, that mineral substances in general are moderated 

 heavy, since that of 233 minerals, whose specific gravity is 

 given by Haiiv (vol. i. p. 261), there are 133 between 3,000 

 and 4,000, and only 46 which are between 4,000 and 6,000. 

 By describing a mineral thus, native sulphur, whose specific 

 gravity is 2*0332, and telesia, which weighs 3*9941, would 

 be included in the same expression. 



The estimation of the angles is given with a precision 

 worthy of that which characterizes the estimate of the spe- 

 cific gravity. An angle is very obtuse when it is greater 

 than 120°; obtuse, if it is from 100° to 120° ; a little obtuse, 

 from 90° to 100°; right, if it exceed 90°; very acute, be- 

 tween 45° and oo° ; acute, when it is 45° • and very acute, 

 when it is less than 45°. (Brochant, vol. i. p. 97.) Thus 

 we learn that a right angle is that which has more than 90°. 

 I have heard M. Werner say, (and I have written his lectures 

 as he delivered them,) that a difference of 10° did not pre- 

 vent him from considering any angle as a right angle : thus 

 we need not be much astonished at seeing cubic zeolite so 

 called [analcime and chabasia, H.], as the great angle of its 

 faces differs but 3° 30' from the right angle. 



WERNERIAN THEORY OF PRIMITIVE FORMS. 



Crystallization is treated as a third article in the particular 

 external characters of solid minerals, under the name of 

 regular external forms. It is observed that there are seven 

 species of principal forms, which may be considered as the 

 nuclei of other forms; and in this point of view they fulfil 

 the same functions as the primitive forms of Haiiy. 



Werner was at perfect liberty in his choice, as he set out 

 on a gratuitous hypothesis. There was no consideration 

 which impelled him to give a preference to such or such a 

 form. He had before him the whole of geometry, with the 

 unlimited permission of choice among all the figures which 

 it possesses in common with mineralogy. We must be- 

 lieve that some principle adopted by reflection would preside 

 at the choice he was about to make, and we can conceive 

 none more worthy of preference than that which corre- 

 sponds with simplicity. 



M. Werner has chosen the icosaedron, or body terminated 

 by twenty faces; the dodecaedron, by twelve ; the cube, by 

 six ; the prism, pyramid, table, by an indeterminate number ; 

 and the lentil, or lens, by two, as it is pretended. The 

 icosaedron is a very complex figure; the prism, pyramid, 

 and table, are in some measure indefinite ; and the lentil, 

 which we are told is composed of two faces, is ; indeed/com- 

 posed 



