LIME. 



215 



CALCAREOUS SPAR. 



Chaux Carbonatfe. Ha^y. — Calcareous Spar. CkaveUmd and Phillips. — Calcareous Spar, or Rhombohedral 

 limestone. Jameson. — Rhomboedriches Kalk-Haloid. Mohs. — Calcaire. Beudant. — (Thomson, Shepard, 

 and Dana include all the varieties of carbonate of lime under the name of Calcareous Spar. I restrict the 

 latter term to the regularly crystallized forms of carbonate of lime, and to those imperfect crystals or masses, 

 which, by cleavage, yield the primary rhombohedron.) 



Description. Colour, of pure varieties, white ; when impure, it is often tinged with vari- 

 ous shades of yellow, grey, red, green, brown, and even black. Streak white and greyish 

 white. It occurs frequently crystallized, and, of all known minerals, exhibits the greatest 

 number of varieties of the rhombohedral series of crystallization. The primary form is a 

 rhombohedron, having angles of 105° 5' and 74° 55' (Fig. 55). When transparent, it is 



Fig. 56. 



Fig. 57. 



doubly refractive, and is then of- 

 ten known by the name of Ice- 

 land Spar. The various secon- 

 dary forms can easily be reduced 

 to the primary, as shown in Fig. 

 56 and 57. Lustre, when pure, 

 splendent and vitreous. Hard- 

 ness 3.0; scratches gypsum, but 

 is scratched by arragonite. Spe- 

 cific gravity from 2 . 50 to 2 . 80. 

 Before the blowpipe, alone, it be- 

 comes caustic lime, and shines 

 with peculiar brightness as soon 

 as all the carbonic acid is driven 

 off; with borax or biphosphate of soda, it fuses with effervescence into a glass. 



Calcareous spar, as well as all the other subspecies under carbonate of lime, may be distin- 

 guished from gypsum by its greater hardness, and by its effervescence in dilute acids. It is 

 not so hard as fluor spar, and it does not, when its powder is thrown into warm sulphuric 

 acid, yield a gas capable of corroding glass. It possesses a less specific gravity than the 

 carbonates of barytes, strontian or lead, each of which it sometimes resembles. 



Composition. Specimen from Iceland — carbonic acid 43.70, lime 56.15 {Stromeyer); 

 carbonic acid 43.05, hme 56.33 {Biot). Formula CaO.COa. 



Geological Situation. Calcareous spar does not appear to be peculiar to any class of 

 rocks. It is found in veins in the granite and gneiss both of northern and southern New- York, 

 while it also abounds in almost all the hmestones and slates in the central and western portions 

 of the State. 



