M I N E R A L G Y. 



487 



ryctogno- 3. The preceding figure, in which the six-planed acnmi- 

 y. nation is folly acuminated with three planes, which 



are set on the acute edges of the six-planed acumina- 

 tion. 



4. Six-sided prism acutely acuminated with three planes 

 which are set on the alternate lateral planes. The 

 apex of the acumination is sometimes more or less 

 deeply truncated. Sometimes the truncation is so 

 deep, that the remains of the acuminating planes ap- 

 pear as truncations on the alternate terminal edges. 

 In other varieties, the prism becomes so short, that 

 the acuminating planes meet and form an acute double 

 three-sided pyramid. 



5. When the planes of the flat three planed acumination 

 N 3. increase so much that those of the six-planed 

 acumination disappear, a six-sided prism is formed, 



Jiatly acuminated with three planes, which are set on 

 the alternate lateral planes in an unconformable posi- 

 tion. When the prism disappears, there is formed an 

 obtuse double three-sided pyramid. 



These prisms are often pyramidally aggregated. 



6. When the prism becomes very low, it may be viewed 

 as an equiangular six-sided table, which is sometimes 

 aggregated in a rose-like form. 



7. Sometimes the six-sided prism is truncated on the 

 lateral edges, and thus forms a twelve-sided prism. 

 The prisms are aggregated in a pyramidal, manipular, 

 scopiform, and tabular manner. 



III. Three-Sided Pyramid. 



It is divided, according to the magnitude of the sum- 

 mit-angle, into the following varieties : 



1. firry obhue three-tided jiyramid, nearly tabular. It 

 is sometimes aggregated in rose-like form. 



2. Flat I hrte~nded pyramid, in which the lateral planes 

 of the one are let on the lateral edges of the other. 

 The angles on the common basis are sometimes trun- 

 cated, and frequently the apices of the pyramid are 

 snore or less deeply truncated. When the truncation 

 on the apices is very deep, the crystal appears as a 

 six-sided table, in which the terminal planes are set 

 on alternately oblique. 



t. Acute three-tided pyramid. This form very nearly 



resembles the cube. 



It would extend this description too much, were we 

 to attempt to give an account of every variety of form 

 exhibited by these crystals ; and besides, we have al- 

 ready enumerated the principal ones. The crystals 

 occur of various magnitudes, as large, small, and very 

 small. The lateral planes of the prisms and pyramids 

 are generally shining, splendent and smooth ; the acu- 

 minating planes frequently streaked or drusy, seldom 

 granulated. Sometimes it occurs in extraneous exter- 

 nal forms of shells, &c. Internally it is generally spe- 

 cular splendent, or shining, sometimes glistening, and 

 the lustre is vitreous, which inclines sometimes to resi- 

 nous, and more rarely to pearly. Fracture perfect 

 conchoid*]. Fragments indeterminate angular, and 

 rather sharp-edged, or they are rhomboidal. Occurs 

 transparent, semi-transparent, and occasionally only 

 translucent. It refracts double *. Brittle, and very 

 easily frangible. 



Chemical Ckaractcrtli is infusible before the blow- 

 pipe, but it becomes caustic, losing by complete cal- 

 cination about 43 per cent. ; effervesces violently with 



Conttituent Parts. 



Oryctogno- 



y- 



limestone. 



100.00 100.00 100.00 100.0000 



r. Gtnxrfi Anmlcn F*p>. Phil. Gthl. Btrfeb, Stiamryrr, Oil- 

 1813, p. S17. MJK. ir. S90. Journ.iv.1lL'. bufiAn. for 



1813, p. !17. 



Geognottic Situation. It never occurs in mountain- 

 masses, but venigenous in almost every rock, from gra- 

 nite to the newest secondary formation. 



An interesting geognestic character of calcareous- 

 spar, is the uniformity of its crystallizations in particu- 

 lar districts. Thus, in the mines of Derbyshire, the 

 acute six-sided pyramid and its congenerous forms are 

 the most frequent and abundant ; at Schneeberg in 

 Saxony, and in the Upper Hart/., the prevailing forms 

 are the regular six-sided prism and table ; while in the 

 mines of Freyberg, the most frequent forms are the re- 

 gular six-sided prism, acuminated with three planes, set 

 on the lateral planes, and the flat double three-sided 

 pyramid. 



Geographic Situation. This mineral is so common in 

 every country, as to render any account of its geogra- 

 phic distribution unnecessary. 



Second Kind. 



GRANULAR FOLIATED LIMESTONE, Jameton Bla't- Granular 

 triger Kurniger Kalkstein, Werner. foliated 



External Character!. Its most common colour is 

 white, grey, red, yellow, and green. Has generally 

 but one colour ; sometimes, however, it is spotted, 

 dotted, clouded, striped, and veined. Occurs massive, 

 and in angulo-granular distinct concretions. Internally 

 alternates from shining to glistening, and glimmer- 

 ing ; lustre intermediate between pearly and vitreous. 

 Fracture foliated, but sometimes inclines to splintery. 

 Fragments indeterminate angular, and rather blunt- 

 edged. More or less translucent. Brittle, and easily 

 frangible. 



Chemical Character*. It generally phosphoresces 

 when pounded, or when thrown on glowing coals. It 

 is infusible before the blow-pipe. It dissolves with 

 effervescence in acids. 



Constituent Parti. Lime, - .56.50 



Carbonic Acid, 43.00 

 Water. - 0.50-100 



liuchok, in Neuen Journal der Chem. iv. s. 419. 

 Geognottic Situation. This mineral occurs in beds, 

 in granite, gneiss, mica-slate, clay-slate, syenite, green- 

 stone, grey-wacke, and rarely in some of the secondary 

 rocks. 



Geographic Situation. This mineral occurs in all the 

 great ranges of primitive rocks that occur in Europe, 

 and in tuch as have been examined in Asia, Africa, and 

 America. 



Viet. All the varieties of this subspecies may be 

 burnt into quicklime ; but it is found, that in many of 

 them, the concretions exfoliate and separate during the 

 volatilization of their carbonic acid, so that by the time 

 when they are rendered perfectly caustic, their cohesion 

 is destroyed, and they fall into a kind of sand, a cir- 



The dcublc refiac-.irg power of calcaiwus-tpu wai fint observed by Erasmus Bartholin. 



