MINERALOGY. 



473 



Genus 1. Honey-stone, 

 i meral resin. 



Genus 1. Coal. 



CLASS III. 

 OSDER I. RESIN. 



Sp. 1. Pyramidal. 



1. Yellow or amber. 



2. Black, including mi- 



neral oil and miner- 

 al pitch. 



COAL. 



Brown coal. 

 Black coal. 

 Glance coal. 



ORDER II. 



S P . 



'2. 

 3. 



to which 

 preceding 

 form 

 spe- 

 charncters 



When we wish to determine the species 

 any mineral belongs, by means of the 

 system, we first ascertain either its nrimuive 

 or cleavage, and afterwards the hardness and 

 cific gravity. We next compare tl 

 with those in the CUsse*. Orders, Genera, and Spe- 

 cies ; and if a species in any of the genera possesses 

 the lime characters, our mineral is to be considered as 

 belonging to that species. 



li the form or cleavage cannot be ascertained, our 

 determination of the species will not be so satisfactory 

 or certain. Thus, suppose we meet with a variety of 

 iron pyrites, in which neither form nor cleavage can 

 he detected, but of which the hardness and specific 

 gravity are known ; and that the hardness is 6, and the 

 specific gravity 49. If we compare these characters 

 with tho-e of the Classes, Orders, Genera, and Spe- 

 cies, we shall find that the only genus to which they 

 apply, i iron l>yitet. But these characters will not 

 enable us to ifeiermine the pecies with absolute cer- 

 tainty, because the esaential character of every pecies 

 depends on the primitive form. They will however 

 shew that the mineral is iron pyrites, evin that it is 

 not rhomboidal iron pyrites ; but they will not enable 

 us to decide whether it is hexahedral or prismatic iron 

 pyrites. In other cases, the pecie can be deternvned 

 without knowing the primitive form ; but i-till, the de- 

 termination is not so certain as when that form i- known. 

 Thus, suppose we meet with a species of magnetic iron 

 ore, which we find by inspection, cannot be either the 

 rhomboidal or prismatic species, but which agrees in 

 hardness and specific gravity with the octahedral spe- 

 cies, we can say that it very probably is a variety of 

 octahedral magnetic ore. Hut there may be a fourth 

 specie* <>f thii genus not in the nystem, having the 

 same barrine** and specific gravity as the octahedral, 

 but with a different primitive form ; and we cannot be 

 certain that our mineral does not belong to that spe- 

 cies. When the prim live form is known, all doubt 

 vanishes. In compound minerals, it is very often im- 

 po-sible to determine the external form. In such caes, 

 a knowledge of the cleavage is of infinite importance, 

 But when neither form, nor hardness, nor specific gravi- 

 ty, ran be determined, the system cannot beadvantage- 

 ouly u*ed ; for the principal characters on which it 

 depends are wanting Amianthus, which is a variety 

 of itraight-rdget) augite. (hornblende,) occurs in crys- 

 tals v.\er\ minute, that they cannot be determined 

 either by the eye or the microscope, and of course the 

 cleavage is not v isible. These crystals are flexible, and 

 their hardness not capable of being determined. Their 

 surface is so considerable in comparison of i heir mass, 

 that they float on water, although they huve a consi- 

 derable specific gravity It u remarked, that in other 

 varieties ot straiglit-rilged augile, the crystals become 

 thicker, then We their flexibility, but are still too 

 VOL. xiv. r*x ir. 



small for allowing the hardness to be ascertained ; Oryctogno- 



others, again, are thicker, but still, owing to their mi- v _^' . 



nuteness, the dimensions of the form cannot be mea- 

 sured ; these sink in water, scratch gypsum, but break 

 on caK-areous spar. At last, in other varieties, the form 

 is discernible by the cleavage, and the hardness is equal 

 to 5 and 6, and the specific gravity equal to 3.0. These, 

 on examination, prove to be straight-edged augite. 

 What these are, so are all the preceding varieties, and 

 also amianthus. It is by pursuing this mode of examina- 

 tion, that we are able to refer such substances as ami- 

 anthus to their true place in the system. Other mi- 

 nerals, again, which occur in an earthy state, can only 

 be referred to their true place in the system, by tracing 

 them in connection with compact minerals, which stand 

 in connection with others having a crystallized struc- 

 ture. Thus porcelain earth can be traced to compact 

 felspar, and this to foliated felspar ; or it can be traced 

 immediately to foliated felspar, and in this way its true 

 place is ascertained. Other earths, and loosely aggre- 

 gated minerals, as many clays, cannot be referred to 

 any species ; these, therefore, are determined in an 

 empirical way ; and we may use the blowpipe, acids, 

 and other means, for obtaining a knowledge of their 

 properties. These bodies are more properly objects of 

 geological curiosity, and of economical value, than in- 

 terexting to the mineralogist. 



The nomenclature of the species used in the present 

 arrangement, is founded on th<- primitive forms of the 

 minerals, on the nature of their cleavage, or on the 

 position of the bevelrnent. 



According to Mohs, all the regular forms in the mi- 

 neral kingdom are reducible to some one of four great 

 sytt' ms or groupes, named rhomboidal, pyramidal, 

 pnsmaticsJ, and hexnhedral or tessular, including 

 octahedron, cube, rhomboidal dodecahedron, Sec. 

 Thus, in the genus corundum, there are three species, 

 in which the primitive forms are the octahedron, rhom- 

 boid, and pri-m ; and hence these are named, octahe- 

 dral corundum, rhomboidal corundum, and prismatic 

 corundum. In the uenu zeolite, there are seven spe- 

 cits; one of the-c is named pnsmatoidal zeolite, be- 

 cause the cleavage is pri-matoidal ; another is named 

 axifrangible, because one of its most striking characters 

 is its axifrangible cleavage. In the genus augite, one 

 species is named oblique- edged augite, because the edge 

 formed by the meeting of the bevelling planes, on the 

 extremities of the ci\>tal, is placed obliquely to the 

 axis of the prism ; another species is named straight- 

 edged augite, because the edge formed by the bevelling 

 planes on the extremity, is straight or perpendicular 

 to the axis of the pri.-m. 



CLASS I. 



If solid there ii a sensible taste. No bituminous CLASS I. 

 smell. Specific gravity under S.O. 



OUI>ER I. GAS. 



.(triform. Not acid. Sp. gr. = 0.0001. 0.00 14. , rd " r - 

 GENUS I. MARSH GAS. 



Smell. More or less respirable. Sp. gr. = 0,0001. MarhGa. 

 0,0014. 



This genus contains three ipecie, vis. 1. Carburet- 

 ted marsh gas. 2. Sulphuretted marsh gas. 3. Pho>. 

 phuretied marsh gas. 



1. Carburetted marsh gas, or carburetted hydrogen. 

 Empynumatic smell. Sp. gr. = 0,0008. 



GrvgHostic Situation This gas rises from marshes 

 and volcanoes. It is also met with in great quantities 

 in coal-mines, forming thejlre-damp of miners. 

 3 o 



