3i4 On Crystallography, 



sence of a foreign substance which has altered the metal 

 ifself. 



I have met with naturalists, however, who, admitting the 

 variations to which the colour is subject, with respect to 

 one part of the minerals, do not warrant us in attaching 

 much importance to the character v^hich it furnishes; as 

 much because it is that which first speaks to the eyes, as 

 because there is always, according to them, relatively to 

 each substance, a colour which is predominant, and which 

 agrees with the greatest niunber of varieties. But the 

 more the observations shall be mukiplied, the more fre- 

 qnenily will it happen that this character will not speak 

 to the eve, except to deceive it and make it take the chancre. 

 No further proof of this is requisite than what happens 

 with respect to the emerald. Grass-green seems long to 

 have been ranged among the general characters of this sub- 

 stance, and, in short, it is not astonishing that every thing 

 which was emerald was of thp same colour. We were not 

 acquainted with any thing else, properly speaking, under 

 this name, than the crystals from Peru, which being form- 

 ed in the same circumstances had received the impression 

 of the same colouring principle. A discovery in which 

 mineralogy and chemistry have concurred, unites the beryl 

 with the emerald ; and from his moment we have emeralds, 

 some greenish-yellow, others blucish, and others of a de- 

 cided yellow; and the number of the crystals of these dif- 

 ferent tints, particularly of the first, which exist in our cot- 

 lectjons, far exceeds the ancrent emeralds. The jargon 

 of Ceylon identified with the hyacinth, according to the 

 analysis of Klaproth, has also disturbed this fast substance 

 in the place it occupied, namely, that of being exhibited of 

 an orange brown colour oidy, excepting in, one variety which 

 was whitish : and it would be as easy to adduce other ex- 

 amples of this kind*, as it is to foresee from the moment 

 that these examples will still continue to be multiphed. 

 The indication of the colour, in the case of the latter being 

 owing to an accessary principle, ought therefore to be dis- 

 missed from the specific character ; and wc shall have a 

 new reason to exclude it, if we consider that every thing 



* Laiinoy brought from Spain several small orange crystals which be- 

 long- to phosphated lime, known in Germany by the name of spar^el-sfnti, 

 bec^.usetlie colour of tlie variety of this substance found at first in the same 

 country inclines to that of asparagus Messrs. Abildgaard and Mant hey 

 have since given me some crystals of this substance which are ireuuently 

 met wifh in certain granitic roCks of Norway, and the colour of which. 

 is iometimes of a greenish blue, sometimes brown, 6c c 



which 



