Schaller — Siderite and Barite from Maryland. 365 



FeO 62-01 (calc — 62-07^ FeO) 



MnO.- none 



CaO none 



MgO none 



The crystals are therefore pure iron carbonate and well 

 suited for obtaining crystallographic constants for siderite. 



Crystallographic Properties. — The siderite crystals have 

 a rather unusual habit for that mineral, as the dominant form 

 is the scalenohedron v= 121311, the common form for calcite. 

 A number of other forms are present, and a very marked 

 feature of these crystals is that in approximately the places 

 where the «-face would come there are rounded hollows. The 

 crystals are highly polished and seemed likely to give perfect 

 reflections, but on examination on the two-circle goniometer, 

 it was found that the faces were not as perfect as was at first 

 expected. This is due chiefly to the fact that some of the 

 large scalenohedral faces appear broken and the parts slightly 

 displaced, yielding more than one signal, several minutes apart. 

 The crystals were mounted in polar position, and so adjusted 

 that on turning the vertical circle (the horizontal one being 

 clamped) the reflections from the several faces of each form 

 fell, respectively, in a vertical line coinciding with the vertical 

 cross hair.. After the crystal was adjusted as perfectly as possi- 

 ble, the reading on the horizontal circle was taken for each 

 face, the signal being brought to the exact center of the field 

 in each case. The forms present are shown in the following 

 table, those forms which are new for siderite being marked 

 with an asterisk. 



r 1011 



n 7075 



*Jc 5052 



/ 0221 



v 2131 



*y 3251 



The new form l=\7075] occurs but once as a small face 

 below { 1011 1 but larger than that face. The reflection was fair. 



<f> p 



raeas 0° 14' 52° 49' 



calc* 0° 00' 53° 07' 



The form &=|5052| occurs as a minute line face somewhat 



rounded, and truncating the edges of the scalenohedron v = 



\ 2131 \. The measurements show that the p angle is about 



68°, though no accurate measurement could be obtained. 



calc. ( P ) = 67° 12'. 



* From element derived by writer. 



