47G 



CRYSTALLOGRAPHY. 



Crystalline 



Form*. 



Pi »TE 



(XXXV. 



: ... us. 



i'.'.V. 



Spoda- 

 :naic. 



White->rtJn 

 pyrites. 



Arsenical 



pyritis. 



ccxxv. 



Fig, 26. 



Mulyb, 



iie:ia. 



Ri:ht qua- 

 drangular 

 jirisn., base 

 an oblique 

 parallelo- 

 gram. 



Gypsum. 



Fig. 27. 



Pistazite. 



Plate 

 CCXXVI. 



Wgs. I, 2. 



-Axinite. 



ffig. 3. 

 Jfcclase. 



similar to that represented in Fig. 25. The symbol for 

 v Inch is M 'H 1 T P. 

 M r TP 



S. Tflfc. The primitive form of this species, and 

 the crystalline forms which it assumes, are exactly the 

 same with those of mica ; yet it is necessary to consider 

 them as distinct species, because their composition and 

 external characters differ. 



!). Spodumene or Iriphanc. This mineral occurs in 

 the mine of Uto in Sweden, and has not hitherto, as far 

 us we know, been observed in crystals. 



10. White-iron pyrites. We noticed this species be- 

 fore when speaking of common cubic pyrites. 



1 1. Arsenical pyrites, or mispickel. Arsenical iron of 

 Hauy. About six varieties of form of this species are 

 known. One of the most common, (not reckoning the 

 primitive form,) is that represented in Fig. 26, called 



6 



ditetrahedre by Hairy ; the symbol for which is M E. 



M r 



12. Molybdena. It seldom occurs crystallized. Crys- 

 tals sometimes occur similar to the crystal of mica, re- 

 presented in Fig. 25. Schmeifser describes a crystal 

 consisting of a six-sided prism, terminated at both ends 

 by a six-sided pyramid. 



V. Right quadrangular Prism, Base an oblique Paral- 

 lelogram. 



This form belongs to three species of minerals. We 

 believe that there is a fourth species ranked by Hauy 

 among prisms with a rectangular base, which really 

 ought to be placed here. The species are : 



1. Gypsum, or sulphate of lime The primitive form 

 of this species, is a pretty tall quadrangular prism. 

 The most common variety of its crystals is the trapc- 

 zienne of Hauy, represented in Fig. 27 ; the symbol for 



which is C E P. 



.f lV . 



2. Pistazite, or epidote, and zoisite. This is a very 



common mineral, though it occurs very frequently in 

 an amorphous form. The most common varieties of its 

 crystals which we have been accustomed to see, are re- 

 presented in Fig. 1, 2. The symbol tor the first is 



i 



T M 'G 1 B, the symbol for the second TM'G'CBEP. 

 TM r z TM r o z eP 



3. Axinite, or thummerstone. This mineral is named 

 from the resemblance which its crystals have to the 

 shape of an axe. Though a good many varieties have 

 been described, they all bear a close resemblance to 

 each other. The most common form is represented in 



Fig. 3. Its symbol is C B 6 P. 

 r u s P 



4. We believe that euclase, which is described by 

 Hauy as having a rectangular base, has, in fact, an 

 oblique base, and therefore should be placed here. 

 But the mineral is so scarce that it is difficult to exa- 

 mine it. 



Oblique 

 quadran- 

 gular 



lirism, with 

 n rectangu- 

 lar base. 



Ho rax. 



VI. Oblique quadrangular Prism, with a rectangular 

 Base. 



To this primitive form belongs only one species, 

 namely borax or subborale of soda. We have never 

 seen any natural specimens of it crystallized with any 

 regularity. But by artificial crystallization it may be 

 obtained under a variety of forms. It usually assumes 

 the form of a six-sided prism. 



VII. Oblique quadrangular Prism, Base a rhomb. 



To this primitive form belong five species ; namely, 



1. Glauberite. This mineral, hitherto found only in 

 Spain, is composed of nearly equal weights of anhydrous 

 sulphate of hme and anhydrous sulphate of soda. Its 

 base is a rhomb, with angles of 75° 32' and 104° 28'. 

 Hitherto only one variety of form has been observed. 

 It is an oblique very flat prism, putting one in mind of 

 the common variety of axinite. 



2. Amphibole, including hornblende, actinolite. gram- 

 matite, tremolitc. This is one of the most abundant 

 mineral species. Hornblende is dark green, almost 

 black ; actinolite usually a lighter green ; and tremolite 

 almost white. The crystals are usually four or six 

 sided prisms. One of the most common varieties is 

 represented in Fig. 4; the symbol for which is 



M 'G 1 P B. 

 M x P r 



3. Augite, or pyroxene, coccolite, diopside, salite. 

 This is also a very common species, occurring abun- 

 dantly in trap rocks. The crystals are not very numer- 

 ous in point of variety of form. One of the most com- 

 mon varieties is represented in Fig. 5. The symbol 

 for it is M 'H' E 1 J E. It is the bisunitairc of Hauy. . 



Mr * 



4. Gadolini'e. Hauy has announced, that the pri- 

 mitive figure of this mineral is an oblique rhomboidal 

 prism. We have never had an opportunity of seeing it 

 crystallized. 



5. Orpiment, or sulphurct of arsenic. Hauy has late- 

 ly ascertained, that the primitive form of sulphuret of 

 arsenic, both red and yellow, is the same ; namely, an 

 oblique prism with rhomboidal bases, the angles of 

 which are 72° 18' and 107° 42'. See Ann. du Mus. 

 d'Hist. Nat. vol. xvi. p. 19. Hence these two sub- 

 stances, if their composition prove different, will con- 

 stitute another anomaly in the theory of crystalliza- 

 tion. 



Crystalline 

 b'orms. 



Oblique 

 quadran- 

 gular 



prism, base 

 a rhomb. 

 Glaub€rite. 



Amphi- 

 bole. 



Plate 



ccxxvr. 



Fig. 4.- 



Au"ite. 



Fig. 5. 



Gadoliniie. 



Orpiment. 



VIII. Oblique quadrangular Prism, Base an oblique 

 Parallelogram. 



To this primitive form belong three species of miner- 

 als ; namely, 



1. Felspar. This is perhaps the most abundant miner- 

 al in nature. It occurs crystallized in a considerable 

 variety of forms. Perhaps that represented in Fig. 6. 

 is the most useful to be known. Its symbol is G 1 T P. 



I TP 



2. Cyaniie, or disthene. This mineral occurs most 

 commonly without any regular crystallization. Four 

 different varieties have been described. One of the 

 most common is represented in Fig. 7. 



3. Sulphate of copper. A variety of crystalline forms 

 of this salt have been observed ; but by far the most 

 common is the primitive form represented in Fig. 8, 

 and the perihexcedre of Hauy, represented in Fig. 9. 

 Its symbol is M 'H 1 T P. 



M n TP 



IX. Rhomboid with ati obtuse Summit. 



Oblique 

 quadran- 

 gular 



prism, base 

 an oblique 

 parallelo- 

 gram. 

 Felspar. 

 Fig. 6. 



Cyanite., 



Fig. 7. 



Sulphate of 

 copper. 

 Fig. 8. 



Fig. 9. 



Rhomboid 

 with an ob- 



To this primitive form belong eight species of miner- tuse sum- 

 als ; namely, 



1. Carbonate of lime, Or calcareous spar. 

 at the summit is 105° 5'. This is the most prolific of onhneT' 

 all known minerals in the variety of forms. The fol- 

 lowing are the most common varieties : — 1. The equiaxe, 



4-. 



The angle Carbonate 



