LIME. 



235 



MARL. 



This substance, which, when pure, contains little else than carbonate of lime, has already 

 been noticed in detail (see page 83). 



ARRAGONITE. 



[From its having been first found in the province of Arragan in Spain.] 



Arragonitc. Hauy, Clcavdand, Phillips, T/unnson a.nd Skcparil. — Prismatic Limestone. Januson. — Prisma- 

 tischcs Kalk-Haloid. Mohs. — (It has also been called Igloitc, Flos Ferri, and Needle Spar. Beudant places 

 it as a subspecies under Carbonate of Lime.) 



DESCRiPTiojf. Colour usually white, but sometimes with a shade of grey, yellow, green 

 and blue. It occurs regularly crystallized ; also in prismatic concre- 

 tions, and massive. The primary form is a right rhombic prism. 

 Fig. 101. M on M' 116° 5' {Phillips). Three of the crystals are 

 often grouped together so as to constitute a si.x-sided prism. Cleavage 

 parallel with the lateral planes of the primary. Fracture conchoidal, 

 passing into uneven. Lustre vitreous, inclining to resinous. Trans- 

 parent and translucent. Brittle, and even frangible. Hardness from 

 3.5 to 4.0. Specific gravity from 2.92 to 2.94. Thin fragments of 

 transparent crystals decrepitate in the flame of a candle ; other varie- 

 ties lose their transluccncy, and become friable. Witli borax, it dissolves, and forms a trans- 

 parent glass, which crystallizes on cooling ; but in soda, it is insoluble. It phosphoresces on 

 hot iron, and dissolves with effervescence in nitric and muriatic acids. 



Arragonite oftentimes so closely resembles calcareous spar, that it is very dilBcult to distin- 

 guish it. The crystalline form, when it can be determined, is always a safe guide. The 

 specific gravity of arragonite is also higher than that of calcareous spar. The blowpipe 

 characters cannot, I think, in all cases be depended on. 



From the fact that some of the foreign specimens of arragonite are fibrous, many of our 

 fibrous carbonates of lime have received that name in American cabinets. But I have reason 

 to believe that arragonite is rare in the United States ; there are certainly but few localities of 

 it in the State of New-York. 



Composition. The chemical composition of this mineral tloes not differ from that of cal- 

 careous spar, except that it contains, in most instances, minute, but very variable, proportions 

 of water and of the carbonate of strontia. In ten analyses of Stromeycr, the water varies 

 from 0.154 to 0.599, and the carbonate of strontia from 0.509 to 4.013. It is now, how- 

 ever, ascertained that these last ingredients are not always present, and that the peculiar 

 crystalline form of this mineral is not due to them. Indeed, M. Gustave Rose has shown 

 that arragonite may be prepared artificially, without the addition of a particle of strontia. 

 When a simple solution of carbonate of lime in carbonated water is evaporated in a water 



