496 



MINERALOGY. 



Granular 

 Dolomite. 



Oryctogno- First Kind. 



CRAKULAR DOLOMITE, Jameson. 

 This is again divided into White and Brown Granu- 

 lar Dolomite. 



External Characters. Colours snow-white, greyish- 

 white, and rarely pale ash-grey. Occurs massive 5 also 

 in small and fine granular distinct concretions, frequent- 

 ly so loosely aggregated, that they can be separated by 

 mere pressure of the finger. Internally glimmering, 

 approaching to glistening, and lustre pearly. Fracture 

 in the large imperfect and slaty, in compact varieties 

 small splintery, which passes into uneven. Fragments 

 indeterminate angular, and blunt-edged. Faintly trans- 

 lucent, or only translucent on the edges. Brittle, and 

 easily frangible. 



Chemical and Physical Characters. It effervesces 

 very feebly with acids, a character which distinguishes 

 it from granular limestone. 



St Gothard. 



Const. Parts. Carbonate of Magnesia, 4'.',.50 

 Carbonate of Lime, . 52.08 

 Oxide of Manganese, . 0.25 

 Oxide of Iron, . 0.50 



Loss, . . . 0.75 TOO 



Klaproth, Beit. b. iv. s. 209. 



lona. 



Carbonic Acid, . . 48 00 

 Lime, . . . SI. 12 



Magnesia, . . . 17-06 

 Insoluble Matter, . 4.00 



Tennant, Phil. Trans, for 1799. 



Gfognmlic Situation. It occurs principally in pri- 

 mitive mountains. 



Geographic Situation. Europe. Beds of dolomite, 

 containing tremolite, occur in the island of lona; and 

 it is found in many countries on the Continent of Eu- 

 rope. 



America. Province of New- York, with tremolite. 

 Asia. Bengal, with imbedded tremolite ; also in Si- 

 beria. 



Uses. Tt appears to have been used by ancient 

 sculptors in their finest works. 



Observations. It is named Dolomite, in honour of 

 the celebrated French geologist Dolomieu. 



Brown Do. * BROWN DOLOMITE, or MAGNESIAN LIMESTONE OF 

 lomite. Tennant. 



Tennant, Transactions of Royal Society of London fur 

 1799. Thomson, Annals of Philosophy Jor December 

 1814. 



External Characters. Colours yellowish-grey, yel- 

 lowish-brown, and a colour intermediate between ches- 

 nut-brown and yellowish-brown ; seldom bluish-grey. 

 Occurs massive, and in minute granular concretions. 

 Internally glistening or glimmering, and the lustre be- 

 tween pearly and vitrjeous. Fracture splintery, and 

 sometimes flat conchoidal. Fragments indeterminate 

 angular, and rather blunt-edged. Translucent, or 

 translucent on the edges. Semihard ; is harder than 

 calcareous-spar. Is brittle. Specific gravity of the 

 crystals, 2.823, 'I 'cnnanl. 2.777, 2.820, Berger. 2.791, 

 Thomson. 



Chemical Characters. It dissolves slowly, and with 

 but feeble effervescence, in nitrous acid. 



Building Hill, near Sunderland. 

 Const. Parts. Carbonate of Lime, 56.80 

 Carbonate of ' magn esia, 40. 8 <t 

 Carbonate of Iron, 0.36 

 Insoluble Matter, . 2.00 100.00 

 Thomson, Annals of Phil. vol. iv. p. 416". 



Geognoslic Situation In the north of England it 

 occurs in beds of considerable thickness, and great ex- 

 tent, and appears to rest on the Newcastle coal-forma- 

 tion ; but in the Isle of Man, it occurs in a limestone 

 which rests on grey.wacke, and contains imbedded por- 

 tions of quartz, rhomb-spar, and sparry-iron. It occurs 

 in trap-rocks in Fifeshire. 



Geographic Situation. It occurs in Nottinghamshire, 

 Derbyshire, Northamptonshire, Leicestershire, Nor- 

 thumberland, and Durham: also in Ireland, at Portum- 

 na in Galway, Ballyshannon in Donnegal, Castle Island, 

 near Killarney. 



Use. Like common limestone, it is burnt and made 

 into mortar, but it remains much longer caustic than 

 quicklime from common limestone ; and this is the 

 cause of a very important difference between magnesian 

 and common limestone, with regard to their employ- 

 ment in agriculture : Lime, from magnesian limestone, 

 is termed hot, and when spread upon land in the same 

 proportion as is generally practised with common quick- 

 lime, greatly impairs the fertility of the soil ; and when 

 used in a greater quantity, is said by Mr. Tennant to 

 prevent all vegetation. 



Observations. A flexible variety of Dolomite occurs 

 in England. The following account contains all the in- 

 formation we possess in regard to it : 



FLEXIBLE DOLOMITE, Jameson. 



External Characters. Colour yellowish-grey, pass- p| cxib i e 

 ing into cream-yellow. Occurs massive. Is dull. Frac- Dolomite. 

 ture earthy in the small, and slaty in the large. Is 

 Opaque. Yields readily to the knife, but. with difficulty 

 to the nail. In thin plates it is uncommonly flexible. 

 Specific gravity, 2.544, Thomson. This is probably 

 below the truth, as the stone is porous. 



Geographic Situation, It occurs about three miles 

 from Tinmouth Castle. 



Observations. This curious mineral was discovered 

 by our intelligent friend Mr. Nicol, Lecturer on Natu- 

 ral Philosophy. To that gentleman we are indebted 

 for the following particulars in regard to it. He finds, 

 that its flexibility is considerably influenced by the 

 quantity of water contained in it. When saturated with 

 water, it is remarkably flexible ; as the evaporation 

 goes on, it becomes more and more rigid, until the wa- 

 ter be reduced to a certain limit, when the flexibility 

 becomes scarcely distinguishable. From this point, 

 however, the flexibility gradually increases, as the 

 moisture diminishes ; and as soon as the water is com- 

 pletely exhaled, it becomes nearly as flexible as it was 

 when saturated with that fluid. 



Second Kind. 



COLUMNAR DOLOMITE. Stanglicher Dolomit, Klap- 

 roth. 



External Characters. Colour pale greyish-white. Columnar 

 Occurs massive, in thin, long, and straight prismatic Dolomlte 

 concretions. Has an imperfect cleavage. Fracture un- 

 even. Lustre vitreous, inclining to pearly. Breaks in- 

 to acicular-shaped fragments. Feebly translucent. Is 

 brittle. 



From the Mine Tschistagow&koy. 



Const. Parts Carbonate of Lime, - 51 

 Carbonate of Magnesia, 47 



Carbonated Hydrate of Iron, 1 99 

 Klaproth, Chem. Abhandl. s. 328. 



Geognoslic and Geographic Situation*. It occurs in 



