490 



MINERALOGY. 



Blue Vesu- 

 vian lime- 

 stone. 



Oryetogno- shire, Yorkshire, Devonshire, Somersetshire, and Dor- 

 setshire. It is sometimes used as a building stone, 

 and, in want of better materials, for paving streets, 

 and making highways. When, by exposure to a high 

 temperature, it is deprived of its carbonic acid, and 

 converted into quicklime, it is used for mortar ; also 

 by the soap-maker, for rendering his alkalies caustic ; 

 by the tanner, for cleansing hides, or freeing them 

 from hair, muscular substance, and fat; by the farmer, 

 in the improvement of particular kinds of soil; and 

 by the metallurgist, in the smelting of such ores as are 

 difficultly fusible, owing to an intermixture of silica 

 and alumina. 



Second Kind. 



BLUE VESUVIAN LIMESTONE, Jameson. Blauer Ve- 

 suvischer Kalkstein, Klaprolh. 



External Characters. Colour dark bluish-grey, part- 

 ly veined with white. Externally it appears as if it 

 had been rolled ; and the surface is uneven. Fracture 

 fine earthy, passing into splintery. Is opaque. Affords 

 a white streak. 



Const. Parts Lime, . . 58.00 



Carbonic Acid, . 28.50 

 Water, which is some- 

 what am mon iacal, 11.00 

 Magnesia, . . 0.50 

 Oxide of Iron, . 0.25 

 Carbon, . . 025 



Silica, . . 1.2599.75 



Klaprolh, Beit. b. v. s. 96. 



From this analysis, it appears, that the vesuvian 

 limestone differs remarkably in composition from com- 

 mon compact limestone. In common compact lime- 

 stone, ICO parts of lime are combined with at least 80 

 parts of carbonic acid ; whereas in the vesuvian lime- 

 stone, 100 parts of limestone are not combined with 

 more than 50 parts of carbonic acid. Secondly, In 

 common limestone, independent of the water which 

 adheres to it accidentally, as far as we know, there is 

 no water of composition ; but in the vesuvian limestone, 

 there are 1 1 parts of water of composition. 



Geographic Situation. This remarkable limestone is 

 found in loose masses amongst unaltered ejected mine- 

 rals in the neighbourhood of Vesuvius. 



Observations. It is known to some collectors under 

 the name Compact Blue Lava of Vesuvius ; and is 

 sometimes employed by artists in their mosaic work, to 

 represent the sky. 



Third Kind. 



Roestone. 



RoESTONE, 



Werner. 



OR OOLITE, Jameson *. Roogenstein, 



External Characters. Colours brown and grey. 

 Occurs massive, and in distinct concretions, which are 

 round granular ; the larger are composed of fine sphe- 

 rical granular, and sometimes of very thin concentric 

 lamellar concretions. Internally dull. Fracture of the 

 grains fine splintery ; but of the mass round granular 

 in the small, and slaty in the large. Fragments in the 

 large blunt-edged. Is opaque. Rather brittle, and very 

 easily frangible. Sp. gr. 2.6829, 2.6190, Kopp 2.585 

 Breithatipt, 



Chemical Characters. It dissolves with effervescence 

 in acids. 



Geognostic Situation.' It occurs along with red sand- Orycto-mo. 

 stone, and lias limestone. s >-^ 



Geographic Situation. This rock, which, in Eng- "~V~~ 

 land, is known under the names Bath-stone, Ketton- 

 stone, Portland-stone, and Oolite, extends, with but 

 little interruption, from Somersetshire to the banks of 

 the Humber in Lincolnshire. On the Continent of 

 Europe, it occurs in Thuringia, the Netherlands, the 

 mountains of Jura, and in other countries. 



Uses. The Oolite, or Roestone, particularly that of 

 Bath and Portland, is very extensively employed in ar- 

 chitecture ; it can be worked with great ease, and has 

 a light and beautiful appearance ; but it is porous, and 

 possesses no great durability, and should not be em- 

 ployed where there is much carved or ornamental 

 work, for the fine chiselling is soon effaced by the ac- 

 tion of the atmosphere. On account of the ease and 

 sharpness with which it can be carved, it is much used 

 by the English architects, who appear to have little re- 

 gard for futurity. St. Paul's is built of this stone, also 

 Somerset- House. The Chapel of Henry VIII. affords 

 a striking proof of the inattention of the architects to 

 the choice of the stone. AH the beautiful ornamental 

 work of the exterior had mouldered away in the short 

 comparative period of SOO years. It has recently been 

 cased with a new front of Bath-stone, in which the 

 carving has been correctly copied : from the nature of 

 the stone, we may predict, that its duration will not be 

 longer than that of the original. Both Portland and 

 Bath stone varies much in quality. In buildings con- 

 structed of this stone, we may frequently observe some 

 of the stones black, and others white. The black stones 

 are those which are more compact and durable, and 

 preserve their coating of smoke: the white stones are 

 decomposing, and presenting a fresh surface, as if they 

 had been recently scraped. Roestone is also used as a 

 manure, but when burnt into quicklime, the marly va- 

 rieties afford rather an indifferent mortar; but those 

 mixed with sand a better mortar. 



THIRD SUBSPECIES. 

 CHALK, Jameson. Kreide, Werner. 



External Characters. Colour yellowish-white, some- chalk, 

 times passes to greyish-white and snow-white. It is 

 sometimes marked with yellowish-grey. Occurs mas- 

 sive, disseminated, in crusts, and in extraneous exter- 

 nal shapes. Is dull. Fracture coarse and fine earthy. 

 Fragments blunt-edged. Opaque. Writes and soils 

 very much. Soft, and sometimes very soft. Rather 

 sectile, and easily frangible. Adheres slightly to the 

 tongue. Feels very meagre, and rather rough. Spe- 

 cific gravity, 2.252, Muschenbroeck, 2.315, Kinvan. 

 2.657, Watson. 2.2-^6, Breithaupt. 



Chemical Characters. It effervesces strongly with 

 acids. 



Constituent Parts. 



Lime, . SB. 5 

 Carbonic Acid, 43.0 

 Water, . 0.5 



Bucholz, in Gehlen's 

 Journ. b. iv. s. 416. 



Chalk from Gallic : a. 

 Lime, . 47.00 

 Carbonic Add, 33.00 

 Silica, . 7.00 

 Alumina, 9.110 



Magnesia, 8.00 



Iron, . 0.05 



Hacquet. 



Lime, - 53 

 Carbonic Acid, 42 

 Alumina, 

 Water, . 3 



Ktrwan, Min. 

 vol. i. p. 77. 



* JRoetttmCj so named on account of its resemblance in form to the roe of fishes. 



