MINERALS FEOM LILLESHALL, SALOP. 



467 



lying lowest in the stone ; but I have not satisfied myself that this 

 is general. 



Barytes. — Occurs in pink, lamellar, somewhat radiating masses, 

 which cleave easily parallel to the 001 and 110 planes of Miller. 

 At their free surfaces transparent crystals are developed, having the 

 forms 001, 110, and 101. Besides this mode the barytes also occurs 

 in small transparent crystals (J-| inch long). The prisms are 

 chisel-ended, being terminated by the planes 110 and 110 of Miller, 

 while the sides of the prisms are contained by the forms 001 and 012. 



Calcite. — In the uppermost bed, called by the miners " cockles," this 

 mineral occurs in clustered groups of crystals, each crystal being a 

 steep scalenohedron with a rhombohedral summit. The grouping 

 commonly takes the form of a steep three-faced pyramid. The faces 

 of the rhombohedral summits are striated in the direction of a line 

 bisecting the angles formed by the edges of the rhombohedron. Some 

 attempts were made to determine these faces ; but the striations 

 prevented any satisfactory measurement. The clustered crystals of 

 calcite have a beautiful ice-like appearance. 



Some of the calcite in large masses has a pink colour, due to 

 manganese. A portion of this pink calcite yielded 



Manganous oxide (MnO) 1-20 per cent. 



Ferrous „ (FeO) -36 „ 



The calcite also occurs in more or less spherical cavities in the 

 lowest bed of stone ; and these invariably contain the mineral in 

 pointed scalenohedrons (Dog-tooth spar). 



Dolomite. — Is the most interesting mineral of the group. It 

 occurs in nodules, which are apparently made up of a succession of 

 laminae of varying diameters. These laminae crystallize at their 

 edges in minute rhombs with curved faces, resembling pearl-spar. 

 The substance of the nodule is cream-colour, but the crystalline 

 surface is often brown from oxidation. 



The minute rhombs do not admit of measurement. Two samples 

 of the typical nodules freed from calcite were analyzed. 



Carbon dioxide (C0 2 ) 



Ferrous oxide (FeO) 



1*. 



Sp. gr. 2-95. 



2t. 

 Sp. gr. 2-92. 



42-29 

 21-49 



102 

 29-06 



5-96 



44-00 

 12-51 



2-08 



34-35 



764 



Manganous oxide (MnO) 



Lime (CaO) 



Magnesia (MeO) 





99-82 



100-58 



* 1 contained -07 per cent, silica not included. 



t 2 is the mean of two analyses of the same sample, in which the following 

 were the differences from the mean :— C0 2 0-13, FeO 0*17, MnO 006, CaO 0-14 

 MgO 000. 



