[ 342 ]' 



LVI. On Crystallography, By M. ITauy. Trnvslaied 

 from the last Paris Edition of his Traitc de Mineralogie. 



[Continued from p. '277.J 

 OF THE CHARACTERS OF MINERALS. 



>V E understand by the term characters of a mineral, 

 every thing that can be the subject of an observation proper 

 for making it known. We could not refrain, in treating 

 of the mineralogical methods in the preceding article, from 

 giving an idea of the characters which are the soul of the 

 system. But it is necessary to enter into more extensive 

 details on this important subject. 



If we consider the characters relative to the various 

 branches of science which furnish them, we must distm- 

 guish them as physical, geometrical, and chemical cha- 

 racters. 



The physical characters are those the observation of 

 which proouces no remarkable change in the state of the 

 substance which presents them, or with respect to which 

 this change is only a condition necessary for observing an 

 effect which in other respects belongs to physics. Thus 

 the phosphorescence produced by throwing the dust of a 

 mineral upon burning coals, although it occasions an alter- 

 ation in the state of the mineral, wilTbe a physical character, 

 like that which arises from the mutual friction of two 

 pieces of quartz. In cases of this kind, where physics 

 and chemistry are so closely allied that it would be dif- 

 ficult to discern their respective limits; we have had it 

 particularly in view to preserve the analogy of the cha- 

 racters, by bringing together those which give rise to ob- 

 Bervations of a similar nature. 



Properly speaking, we ought to denominate as geome- 

 trical characters those only which are drawn from the de- 

 termination of the primitive fornis, and from the measure- 

 ment of the angles which form by their meeting the faces 

 of the crystals and the sides of these same faces. But we 

 have thought it right to give to this chari^^cter a greater 

 extent than that which seems to agree with it when we 

 take it in a rigorous sense, and to include within it every 

 thing which has a reference to the configuration ; such as 

 the aspect of the fracture, w hich sometinies forms con- 

 vexities and concavities, and «ometimcs presents points or 

 asperities, &c. Besides, we consider, independently of this 

 aspect, the direction in which the fracture takes place, 

 >\hich is soiijetimcs longitudinal, 6r parallel to the axis of 

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