. 84{>. CHARACTERISTIC. 377 



includes an angle of 2 21' in the plane of the short dia- 

 gonal with the perpendicular line erected in the centre of 

 the base. " Inclination = 0" means, either that there exists 

 no inclination at all, or that this inclination has not been 

 as yet attended to in the present determination of the crys- 

 talline forms. 



The angle indicated in horizontal prisms that assume 

 a hemi-prismatic character, is the one contained between 

 the occurring face and the axis, together with the situation 

 of the face by means of the signs + and , agreeably to 



Pr 



. 1 53. For instance, in paratomous Augite-spar, = 



73 54', where the sign + is understood. For designating 

 vertical prisms in hemi-prismatic combinations, the lateral 

 angle is given, which corresponds to that terminal edge of 

 the fundamental form, which occurs in the combinations. 



With respect to cleavage, the expression " Cleavage, R," 

 for instance, in rhombohedral Lime-haloide, means, that 

 this mineral has its cleavage parallel to the faces of a rhom r 

 bohedron, similar to the fundamental form of the species ; 

 " Cleavage, P oo. P 4- oo. [P + w]" in pyramidal Gar- 

 net, means, that this mineral has its cleavage parallel to 

 the faces of two rectangular prisms, and at the same time 

 perpendicular to their axis ; " Cleavage, ?r + os" in pris- 

 matic Chrysolite, indicates, that the cleavage of this mineral 

 is parallel to a plane passing at the same time through the 

 axis and the short diagonal of the prism P + oo ; " Clear*- 

 " age, (Pr + c;) 3 =87 42'. Pr -f oo. Pr + co" in parato- 

 mous Augite-spar, expresses that the individuals of this 

 species may be cleaved, first, parallel to the faces of an ob- 

 lique-angular four-sided prism, of the given angles ; and 

 secondly, parallel to planes, which pass through the axis 

 and both diagonals of the prism P + cc ; or, what comes to 

 the same, parallel to the faces of a rectangular prism. 



Cleavage is sometimes found to be hemi-prismatic or 

 tctartO'prismatic. Paratomous Augite-spar shews an ex- 

 ample of the first. The hemi-prismatic faces of P, express- 



