MINERALOGY. 
of Haiiy's, whofe characters employed for fpecification 
are confined within a far more narrow compafs. The laws 
for framing fpecies in mineralogy, whatever the charac¬ 
ters may be on which they are founded, mult always be 
arbitrary: but, fortunately for the fcience, the different 
opinion's entertained by different fchools refpeCting the 
nature of the fpecies, is a mere matter of fpeculation, 
exerting little or no influence either on the diagnofis or 
the arrangement of mineral lubftances : for, provided the 
natural connexion between two mineral fubflances re¬ 
main undiflurbed, it is certainly of no great importance 
whether one of them be degraded into a mere variety of 
its neighbour, or raifed to the rank of a diftinCt fpecies. 
Werner enumerates three different kinds of affinity of 
minerals, viz. the chemical, depending on the firnilarity 
of their confiituent parts ; the oryCtognoftical, confiding 
in the approximating refemblances of their external cha¬ 
racters ; and the geognoltic affinity, denoting firnilarity 
in occurrence, relative age, &c. The fpecies is fubdi- 
vided by Werner into fubfpecies and variety: by the for¬ 
mer areffneant foffils belonging to the fame fpecies with 
another, but differing from it in two or three particular 
external characters ; the latter is produced by the dif¬ 
ference in any Angle external character, fuch as colour, 
fraCture, &c. 
14. The fyftem of Brochant is formed entirely on the 
principles of Werner’s claffification, and is undoubtedly 
the molt perfpicuous account of the fyftem of the German 
mineralogifl which has yet been publifhed. 
15. Syftem of Schmeiifer; London, 1795. 
16. Syftem of Babington; London, 1796. 
17. The ftudy of the regular forms of minerals has been 
fuccefsfully profecuted by Rome de l’llle, whofe indefati¬ 
gable refearches have eminently contributed to the pro- 
grefs of the fcience of mineralogy in general, and whofe 
Cryltallographie (of which the firft edition appeared in 
1773) is defervedly characterized as the refult of labours 
immenfe in their extent, almofl entirely novel in their 
objeft, and of the higheft importance on account of their 
utility. His claffification of minerals has nothing pecu¬ 
liar ; but for the accuracy, completenefs, and elegance, 
of his defcriptions, and particularly his fcientific method 
of determining the cryflalline forms, he flood unrivalled 
among the mineralogilts of his time. 
18. Haiiy’s Syftem. Several memoirs of Haiiy, illuflra- 
tive of his theory of the flruCture of cryftals, were fol¬ 
lowed, in 1801, by that celebrated profeffor’s great work, 
entitled “Traitede Mineralogie.” In this important and 
truly clafiical production, the new theory of cryftals (of 
which a detailed view is given under the article Crys¬ 
tallography, vol. v.) is alfo made fubfervient to the 
claffification of mineral lubftances. Haiiy has defined the 
mineralogical fpecies “ an affemblage of bodies, the inte¬ 
grant molecules of which are fimilar to each other, and 
have the fame compofition.” According to his mode of 
viewing the lubjeCt, minerals have both a geometrical and 
a chemical limit; the former confilts in the invariable 
form of the molecule, the other in the compofition of the 
fame molecule. Haiiy prefers making ufe of the geome¬ 
trical limit for determining the fpecies, not only becaufe, 
minerals being in general more Or lefs mixed with he¬ 
terogeneous matter, it often happens that the chemical 
limit is but imperfeCtly reprefented by the refults of the 
analyfis, whereas mechanical divifion invariably furnifhes 
the lame form of the molecule; but principally becaufe 
the geometrical limit is far more obvious and palpable, 
fince to obtain it nothing is in many cafes required but 
the mechanical divifion of the cryftal. In cafes where the 
integrant molecule belongs exclufively to a determined 
combination of component principles, it alone is fufficient 
to dillinguifh the fpecies ; but there are forms -of mole¬ 
cules which are common to feveral diltinCt fpecies; and 
thefe forms, as far as they are known, happen to poffefs 
the peculiar character of lymmetry and regularity, con- 
ftituting, as it were, limits with refpeCt to other forms. 
439 
As in this latter cafe the character derived from the inte¬ 
grant molecule is not fufficient, Haiiy adds to it another, 
chemical or phyfical, character for the dilcrimination of 
the fpecies : thus, for inftance, the property of diffolvino- 
in water, fuper-added to the cubic form, determines mu- 
riat of loda, or common fait; but, if the fame form is 
united to the property of becoming eleCtric by heat, we 
have borat of magnefia, or boracite. The type of the 
fpecies, according to Haiiy, being once determined, it is 
comparatively eafy to arrange the varieties of cryftalliza- 
tion belonging to the fame fubftance, by afcertaining, 
with the affiltance of the theory of decrements, whether 
all their forms, even thofe which no longer retain a trace 
of the primitive form, are in exadt correfpondence with 
the latter. With regard to the varieties, fuch as thofe 
compofed of fibrous, granular, or compadt maffes, of 
which the type, though it Hill exilts in them, can no 
longer be determined, their difcrimination depends on 
the phyfical and chemical properties of the fubftance, 
fuch as hardnefs, l'pecific gravity, eledtricity, &c. In what 
regards the genera and upper divifions, the diftribution 
is made after the component parts or chemical properties 
common to all the fubftances contained in the fame divi¬ 
fion. The method adopted by Haiiy, in his defcription 
of the mineral fpecies, is the following. At the head of 
the defcription of each mineral is placed the effential cha- 
radler, founded on the molt conftant properties which 
diftinguilh its individuals; after which follow the phyfi¬ 
cal, the geometrical (comprehending the cleavages and 
primitive form of the fubftance), and the chemical, cha- 
radler; to which is added the diltindtive charadter, in 
which the differences are pointed out that diftinguilh the 
fubftance in queftion from others which might be ealily 
miftaken for it. Thefe general charadters are followed by 
the enumeration of the varieties of form (divided into 
determinable and undeterminable), and the varieties de¬ 
pending on light, fuch as colour, tranfparency, &c. 
The fyftem of Haiiy confilts of four dalles. I. The firft 
clafs confilts of fubftances which are compofed of an acid 
united to an earth or an alkali, and fometimes to both ; 
and it contains four orders : 1. Difengaged acidiferous 
fubftances ; as, fulphuric acid, and boracic acid. 2. Earths 
combined with an acid. 3. Alkalies combined with an 
acid. 4. Earths and alkalies combined with an acid. II. 
This clafs includes only earthy fubftances, but fome¬ 
times combined with an alkali. It conftitutes the fili- 
ceous genera of other lyllems. III. The third clafs com¬ 
prehends combuftible fubftances which are not metals. 
It is divided into two orders ; the firlt containing fimple, 
and the fecond compound, combuftibles. IV. The metals 
form the fourth clafs. It is divided into three orders, 
which are charafrerifed by different degrees of oxydation. 
Befides thefe claffes, there are three appendices. The firft 
contains thofe fubftances whofe nature is not fulficiently 
known to have their places accurately alfigned in the fyf¬ 
tem. The fecond appendix includes aggregates of dif¬ 
ferent mineral fubftances. It is divided into three orders. 
The firft treats of primitive rocks ; the fecond of fecon- 
dary and tertiary rocks ; and the third of breccias. The 
third appendix is devoted to the conlideration of volcanic 
produfts. This is divided into lix claffes ; but it is to be 
obi'erved, that the volcanic products of this mineralogifl: 
comprehend, not only fuch fubftances as are univerfidly 
allowed to have a volcanic origin, but alio balalts, traps, 
and other minerals, the origin of which is Hill queltioned. 
Tableau, comparatif, Paris, 1809. 
19. The lyltem of Brongniart takes a wider range than 
other fyltems, including fubftances which are not treated 
of by writers on mineralogy. It is divided into five claffes. 
The firft contains thofe fubftances, excluding the metals, 
which are combined with oxygen. It contains two or¬ 
ders ; the firft including air and water, and the fecond the 
acids. The fecond clafs, which treats of ialine bodies, is 
divided into two orders ; the firft comprehends the alka¬ 
line falts, and the fecond the earthy falts. The third clafs, 
3 containing 
