76 



common base. The right hand figure represents two pyra~ 

 mids of the same, transversely cut through the middle, 

 showing a plane of 1 2 sides, and turned on the axis till they 

 meet each other in an opposite direction, exhibiting a re- 

 markable appearance, called by some authors macling. They 

 often seem to be two crystals passing into each other, and 

 are then said to be twins. This is formed on a gangue or 

 lump -of manganese, or black wad as the miners term it, 

 which seems to give the crystals a dirty tinge, especially 

 those nearest to it. We do not know that it has any other 

 effect on the crystallization. 



TAB. XXXIV. 



CALX carbonata, var. metastatica. 

 Carbonate of Lime, var. metastatic. 



Class 2. Earths. Order 1 . Homogeneous. 

 Gen. 1 . Lime. Spec. 2. Carbonate of Lime. 

 Div. 1. Crystallized. 

 Var. Crystal metastatic terminating with primitive facets. 



Upper Figures. The metastatic crystallization is form- 

 ed, as before observed, by a particular arrangement of the 

 molecules. These continue to form regularly, according to 

 the supply of those molecules, which, stopping abruptly, 

 terminate in the obtuse point of the primitive crystal, show- 

 ing three faces. This termination is not very common : 

 the outline on the left hand will help to explain it. The 

 other lateral faces will be spoken of hereafter. 



The lower figure shows the equiaxe termination, and 

 the right hand geometrical figure, its formation upon the 

 rhomb. 



