44 THOMAS STERRY HUNT ON A NATURAL SYSTEM IN 



light of modem chemistry, it is possible to devise a uew miueralogical method \Yhich shall 

 retain all that was good in the Natural History System, and at the same time bring it in 

 accordance with the facts of chemistry, thus giving a veritable Natural System to 

 Mineralogy. 



§ 48. The great divisions marked by external characters were made by Mohs and his 

 school the basis of a system of classification, as is exemplified in his orders of Mica, Spar, 

 and Gem, already noticed in § 5-6. We have there seen the heterogeneous nature of the 

 order Spar, wherein — besides the genera, ^'chiller-Spar ; Dislhene-Spar, including cyanite ; 

 Triphane-Spar, comprising spodumene and prehnite ; Petaline-.Spar for petalite ; Azure-Spar 

 for lapis-lazuli and lazulite ; Aitgile-Sjiar, including pyroxene, amphibole, wollastonite 

 and epidote ; Feld-Spar, embracing adularia, albite, anorthite, labradorite and scapolite — 

 there was a genus, Kouphone-Spar, in which were grouped not only leucite and sodalite, 

 but the characteristic zeolites, mesotype, laumontite, harmotome, analcite, chabazite, stil- 

 bite and heulandite. With these was also placed apophyllite, while datolite was assigned 

 to another genus, Di/sionie-Spar. When, in 1844, Shepard divided the order Spab by the 

 separation from it of a new order. Zeolite, he transferred to this the whole of the species 

 of the latter two genera. The order Spar of Mohs, and the united orders of Spar and 

 Zeolite of Shepard thus included alike protosilicates, protopcrsilicates and persilicates of 

 very various degrees of hardness and chemical unlikeness ; since not only datolite, apophyl- 

 lite and pyroxene, bu.t mesolite and stilbite, leucite and albite, siDodumene and epidote, 

 and even cyanite found a place therein. A still more heterogeneous assemblage was 

 seen in Dana's order, Chalcinea, which comprised not only the order Spar of Mohs, but 

 also the protopersilicate micas of his order Mica. 



§ 49. We propose, while keeiwng in view the great chemical suborders already 

 defined in our system, to group mineral species with more regard to these external char- 

 acters than has hitherto been done. The obvious distinctions of structure, hardness and 

 density, which separate protopersilicates like garnet, staurolite, and tourmaline, from the 

 micas on the one hand, and from the feldspars, scapolite and zeolites on the other, though 

 but imperfectly appreciated, underlaid the division by Mohs into Gem, Mica and Spar, and 

 the necessity of a subdivision of the sparry or spathoid type was soon felt by Shepard. 

 The need of this is most apparent in the great suborder of the protopersilicates, where it 

 will be seen that, alike on chemical and physical grounds, the natural line of division coin- 

 cides with that between hydrous and anhydrous species, — the latter including the feldspars, 

 leucite, sodalite and scapolites, and the former or hydrospathoid, the zeolites. A similar 

 distinction of hydrous and anhydrous spathoids is equally marked in the protosilicates. 

 Upon the foregoing distinctions, and upon the still farther one, which in each suborder 

 separates all these crystalline species from amorphous colloid compounds, we may proceed 

 to divide the various suborders into Tribes. 



§ 50. Beginning with the Pkotosilicate!^, we recognize first among them a type of 

 crystalline hydrous species of inferior hardness and comparatively low density, which are 

 decomposed by strong acids with the formation of a jelly, or to vise Graham's phrase, pec- 

 tise with acids. These hydrospathoids, which are represented by pectolite, apophyllite, 

 datolite, calamine, etc., may be conveniently designated as the tribe of the Pedolitoids. A 

 second type, not very dissimilar to the first, but somewhat harder, and anhydrous, though 

 still pectising with acids, is represented by willemite, tephroite, helvite, wollastonite, 



