340 
Mohs^ Syste^ii of' Crystallography 
arising from natural history. On the former principle are fel- 
spar^ augite-spar^ azurr-spar ; on the latter, iron -pyrites^ co- 
halt-pyrites, lead-glance, molyhdenum-glance, and others. No 
doubt, the second class of names have a chemical sound ; but 
they have no chemical meaning; and all depends upmi the mean- 
ing, Of a similar, yet not altogether identical nature, dx^ fluor- 
haloid, calcareous-haloid, gypsum-haloid; but not less excep- 
tionable in that respect. 
16. Apparent exceptions. ^\\\ conformity with zoology and 
botany, the adjunct, by which the name of an order is changed 
into that of a genus, is coupled with th-e original term, and forms 
a compound name, which thus belongs to the genus (IS.) An 
exception from this arrangement seems to take place in the or- 
ders of metals and gems. The name of the order, however, is 
in ' these cases merely suppressed, being sufficiently apparent 
without mentioning. Every one knows that gold, silver, tellu- 
rium, bismuth, &c. are metals; and the generic names, goid- 
metal, silver-metal, &c. could scarcely be tolerated. Such also 
is the case with diamond, topaz, zircon, and others. Diamond- 
gem, topaz-gem, &c. would be awkward terms. The name of 
a metal or of a gem, sufficiently points out the order to which 
the one or the other belongs. 
17. Farther restriction of the Generic Name. — Denomination 
of the Species. — -The farther restriction of the generic names, is 
brought about simply by means of an adjective, indicating the sys- 
tem of crystallizations, or some relation of the cleavage, or in ge- 
neral, that character bv which the species of a genus are most 
advantageously distinguished. Such are hexahedral, prismatic, 
rhomhoidal iron-pyrites ; rhomhoidal, octahedral, prismatic co- 
rundum ; octahedral, rhomhoidal, prismatic iron-ore, and many 
others. When the forms of two species in a genus belong to 
the same system of crystallizations, the same process is followed ; 
to the one adjective is joined another, by which the nature of 
the cleavage is mor^ accurately denoted. This has been done 
in cases such as rhombbidal and prismato-rhomboidal ruby-blend, 
pyramidal and prismato-pyramidal titanium^ore, and the like. 
In these instances, no idea must be entertained of the transposi- 
tion or mingling of two systems of crystallizations. In the lirst 
