150 CHARACTERISTIC. 



question is to be determined. If irregular, but not yielding a form 

 of cleavage, it is merely to be observed whether it be solid, liquid 

 or gaseous. In case the mineral be neither liquid nor gaseous, the 

 next question will be, the degree of hardness it possesses. 



The examination being conducted thus far, the characteristic may 

 be applied, from which we learn the nature of those observations 

 still necessary to be made, before arriving at the end in view. In 

 illustration of the entire process, let us take the following example. 

 Let the mineral be crystallized under the form of the regular rhom- 

 bic Dodecahedron, the cleavage being parallel to the faces of the 

 Cube ; and let its hardness be = 2-5. The information respecting 

 the form of our mineral conducts us to Class I. and Order I. while 

 that relating to its hardness effectually excludes it from No. 1, and 

 those species below No. 7. This group of species, not differing 

 from our mineral in respect to this mark by an amount above unity 

 in the scale, are considered as possessing the same degree of hard- 

 ness. The mineral then belongs to one of these six species. The 

 next characteristic mark to be observed, for the exclusion of those 

 members of the group to which it does not belong, consists of the 

 specific gravity. Let the specific gravity of our mineral be 7-4. 

 This observation separates three of the group, at the same time that 

 it identifies the mineral under examination with one of the remain- 

 ing two, while the other is not excluded by a difference above -5 ; 

 an amount of difference always necessary for perfect exclusion in 

 specific gravity. Another mark is therefore required, to complete 

 the characters of these two species. This mark we find to be con- 

 nected with cleavage. No. 5 is easily cleavable, whereas no re- 

 mark being appended to No. 4, it is not easily cleavable. Let our 

 mineral be easily cleavable. No. 3 is of course excluded, and the 

 mineral under examination is No. 5, Galena. 



Let us suppose another instance. Let the mineral be crystal- 

 lized; the system of crystallization a right rhombic Prism, and hard- 

 ness = 7-5. It belongs, therefore, to Class I, Order X ; and is one 

 of the species contained between No. 45 and the end of the order. 

 Let the specific gravity be =3-5. This excludes all but Nos. 50, 

 51, 52 and 53. The final mark is the inclination of the lateral planes. 

 Let this be M on M 129. This observation proves the mineral to 

 coalesce with Staurotide, while it excludes it perfectly from the re- 

 maining three. 



These are ordinary examples. It will not frequently, however, 

 be found requisite to proceed so far in the characters of many of the 

 species, .excepting the one which comprises the individual ; since 



