A Nor Minerahgical Nomenclature. 11 



the occurring form, llic peculiarity of its cleavage, or some 

 peculiar physical or chemical character. In specifying the 

 crystalline form, the following terms have been employed, viz : 

 cubicus, when the primary is a cube ; octahedrus, when the re- 

 gular octahedron ; dodecahedtus, when the rhombic dodecahe- 

 dron ; rhombohedrus, when the rhombohedron ; pyramidalis, 

 when an octahedron not regular ; prismaticus, when a prism, 

 or more particularly a rhombic or rectangular prism. The 

 several right prisms have been designated by a term indicating 

 the base of the prism ; thus qmdratm, for right square prism; 

 rcctavgulus, rhombicus, rhomboidetis, respectively, for right rec- 

 tangular, rhombic or rhomboidal prisms. The term obliquus 

 lias been restricted to the oblique rhombic prism, the oblique 

 rhomboidal being expressed by the adjective triclinaius, in allu- 

 sion to the three oblique inclinations of its axes. 



Other more general terms have been occasionally employed, 

 depending on the following classification of the primary forms, 

 founded on the relations of their axes : 



Class 1. JMonomelrica, (jaovos one, and (aet^ov measure) : includes 

 the cube, regular octahedron and rhombic dodecahedron, in which 

 the three axes are equal, or of one kind. 



Class 2. Dimclricc*, (<5ig two, and (wrfov) : includes the right 

 square prism and square octahedron, in each of which the axes are 

 of two kinds. 



Class 3. Trimetrica, (rgig three, and (xstjov) j includes the right 

 rectangular and rhombic prisms, and the right rectangular and rhom- 

 bic octahedrons, in which the three rectangular axes arc unequal. 



Class 4. Monoclinala, (fxovo.c one, and xXivw to incline) • includes 

 the right rhomboidal and oblique rhombic prisms in which one of the 

 three axes is obliquely inclined to one of the remaining two. 



Class 5. Triclinata, (rgis three, and xXivw) > includes the oblique 

 rhomboidal prism, in which all three axes intersect at oblique angles. 



Class 6. Tetraxona, (verruga four, and "uguv axis) : includes 

 the hexagonal prism and rhombohedron, which have four axes. 



The relations of the forms, in any one of these classes, is such 

 that it may be impossible in some instances, from an entire indis- 



