478 



CRYSTALLOGRAPHY. 



Crystalline 

 Forms. 



Garnet. 

 Pute 

 CCXXVI. 

 Fig. 20. 



Blende. 



Bl PYRAMI- 

 DAL Dode- 

 cahedron. 



Carbonate 

 of baiytci. 



Phosphate 

 of lead. 



Octahe- 



»R0N. 



.Regular 

 octahe- 

 di on. 



Salammo- 

 niac. 



Fluor spar, 



Alum. 



Spinel 1. 



Diamond. 



Fig. 21. 



Native 

 amalgam. 



■Red cop- 

 per oi e. 



Magnetic 

 iron ore. 



1. Garnet. This species occurs most commonly in 

 the primitive form. We have seen it likewise crystal- 

 lized, as in Fig. 20. The symbol for which is B. 



i 

 n 



2. Blende. It occurs crystallized in its primitive 

 form. Likewise in tetrahedrons and octahedrons. And 

 iu some other forms which are modifications of these. 



V. Crystals whose Primitive Form is the Bipyra- 

 midal Dodecahedron. 



Only two mineral species have this primitive form, 

 and they are both salts ; namely, 



1. Carbonate of barytes. The crystals of this species 

 are small and rare. Hence its primitive form remain- 

 ed long indetermined. It was first supposed by Hauy 

 to be a six-sided prism. We have seen it crystallized 

 in the primitive form in Scotland. The specimen, we 

 believe, was found at Wanlock-head, but we are not 

 certain. 



2. Phosphate of trad. We have seen specimens of 

 the primitive form of this mineral from Cornwall. But 

 it is more commonly crystallized in six-sided prisms. 



VI. 



Crystals whose Primitive Form is the Octa- 

 hedron. 



This primitive form, next to the parallelopiped, is 

 the most extensive in the mineral kingdom. The crys- 

 tals belonging to it may be conveniently distributed 

 into four groups, according to the shape of the octahe- 

 dron. 



L Regular Octahedron. 



This primitive form belongs to eleven species of mi- 

 nerals ; namely, 



1. Salammoniac. This mineral, as far as we know, 

 has never been observed crystallized in a native state. 

 But by artificial crystallization, it has been obtained in 

 regular octahedrons, in cubes, and in a figure bounded 

 by twenty-four trapezoids, somewhat like the leucite 

 crystal. 



2. Filiate of lime, Fluorspar. This mineral occurs 

 usually crystallized in cubes ; though we have seen 

 specimens of it crystallized in the primitive form. 



8. Alum. This salt almost always occurs in octahe- 

 drons. Sometimes it takes the cubic form, but very 

 rarely. The cubo-octahedron also sometimes occurs. 



4. Spinelt, including Ceylanite and Auiomalite. This 

 mineral likewise almost always has the primitive form. 

 Sometimes the edges are truncated in consequence of a 

 decrement of one range parallel to the edges. 



5. Diamond. This mineral assumes a considerable 

 number of crystalline forms,- we have seen at least 30; 

 but no description of them has yet been published. It 

 occurs often in octahedrons, and often likewise with 

 48 spherical faces, as represented in Fig. 21. 



6. Native amalgam. This rare mineral occurs usu- 

 ally in regular octahedrons It is said that it has been 

 observed likewise crystallized in rhomboidal dodecahe- 

 drons. 



7. Red copper ore, or Protoxide of copper. It is most 

 commonly crystallized in octahedrons, sometimes in 

 .cubes, sometimes in cubo-octahedrons. 



& Magnetic iron ore, or Deutoxide of iron. The crys- 

 tals of this mineral are usually octahedrons ; sometimes 

 it occurs in rhomboidal dodecahedrons. 



9. While oxide of arsenic. Tie only crystals of this Crystalline 

 mineral hitherto observed, are regular octahedrons. Form?. 



10. Native bismuth. Hauy has ascertained, by me- „;". ~~' 

 chanical division, that the regular octahedron is the ; de ot - ars ^ 

 primitive form of this species. It has been observed nic. 



in regular crystals of three forms : 1. Regular octahe- Native bis- 

 dron. 2. Cube. 3. Rhomboid, with angles of 60° and mutjj. 

 120°. See Hauy, Ann. duMus. d'Hist. Naturelle, torn. 

 xii. p. 198. 



11. Native antimony. We have seen specimens of Natlre an- 

 this mineral from the mine of Salu in Sweden. But "m°ny. 



it is very scarce. We do not know that it has ever 

 been observed crystallized. But Hauy has ascertained 

 its primitive form by mechanical division. 



II. Pyramids having a rectangular Base. 

 This primitive form belongs to 12 species of minerals; 



Pyramids 

 having; a 

 rectangu- 

 lar base. 



Nurate of 

 potash. 



namely, 



J . Nitrate of potash. This salt sometimes occurs 

 Crystallized in its primitive form, but much more com- 

 monly in six-sided prisms, often terminated by six-sided 

 pyramids. 



2. Sulphate of soda. This salt occurs crystallized in Sulphate of 

 a good many forms. Rome de Lisle gives the fullest ^d*. 



and best account of its crystals that we have seen. The 

 common crystals are in four or six-sided prisms, and so 

 much channelled and irregular, that it is scarcely pos- 

 sible to determine their angles. 



3. Lomonite. But few crystallized specimens cf this Lomocite 

 mineral have been hitherto observed, Flauy has de- 

 termined its primitive form, and described some of its 

 varieties in his Tableau Comparatf, p. 49, and 195, 



to which we refer the reader. 



4. Chiastolite, or Hollow-par ; Made of Hauy. Wer- Chiastolite-. 

 ner considers this mineral as a sub-species of felspar. 



But Hauy has ascertained that its primitive form is the 

 octahedron. It occurs usually in four-sided prisms. 



5. Arragonite. This species ha9 long puzzled the Arraga. 

 Abbe Hauy. Its constituents are the same as those of nite. 

 calcareous spar, but its properties are different. He 



has at last put it into his system as a peculiar species. 

 The fullest description of its crystals is given by Bour- 

 non in his Miner a logic, to which we refer. 



6". Topaz. Hauy at first conceived the primitive Topa«. 

 form of the topaz to be a parallelopiped, consisting of a 

 right prism, with rhomboidal bases. But he afterwards 

 ascertained that it is an octahedron, and the same with 

 that of shorlous beryl, to which he has in consequence 

 united it. It occurs most frequently in eight-sided 

 prisms, similar to Fig. 22. 



7. Yenite. This very scarce mineral has been hitherto Yeiute! 

 found only in the Isle of Elba. Hauy, in his Tableau 

 Comparalif, has announced the octahedron as its pri- 

 mitive form ; and Cordier, the discoverer of the mine- 

 ral, has described five varieties of crystal in the Jour, 



des Min. vol. xxi. p. 65. 



8. Carbonate of lead. This mineral occurs crystal C-rbonate 

 lized in octahedrons, and likewise in bipyr midal do- ol lead * 

 decahedrons, and six-sided prisms. 



9. Sulphate of lead. The most common form of the Sulphate 9 

 crystals of this salt is the octahedron, though it oc lead, 

 curs also crystallized in various other very irregular 



forms. 



10. Muriate ofco/rpcr. This salt was brought origi- Afuriate erf 

 nally from South America. It has been observed also copper. 



in the lava of Mount Vesuvius. The primitive form 

 is the octahedron, and three varieties of crystals have 

 been described. 



11. Arseniale of copper. This mineral, found first Arser,ia,e 



■' 1 1 of copper. 



Plate 



cexxvr. 



Fig. 22. 



