Schaller — Siderite and Barite from Maryland. 369 



Barite. 



The barite occurs in three different forms on the specimens 

 seen by the writer. The first is the white massive form which 

 is often imbedded in the matrix. It is usually opaque and 

 shows good cleavage. The second form occurs as an opaque 

 white efflorescence which is composed of an aggregate of min- 

 ute crystals. The third form is present in transparent color- 

 less crystals which often reach a length of several millimeters, 

 though usually they are rather smaller. The largest ones seen 

 were about a centimeter long and 1 to 2 mm thick. On some 

 specimens these transparent crystals are attached by one end to 

 the massive barite and form a fringe, as it were, around it, the 

 crystals standing normal. This occurrence is very suggestive 

 of a secondary formation of the crystals, they being derived 

 from the massive barite in the matrix. The large clear crys- 

 tals are probably a more perfect development than the white 

 efflorescence and both are doubtless derived from the massive 

 barite. In the massive barite there are no siderite crystals, 

 though small fragments of the matrix are included therein, and 

 in the efflorescence there are frequently found enclosed crystals 

 of siderite, and the clear large barite crystals are intermingled 

 with those of siderite. 



The crystals of barite are of especial interest as they are of 

 an uncommon habit ; they are prismatic, elongated parallel to 

 the vertical axis. Such crystals have been noticed several 

 times but are not the common form for barite. 



The faces of the crystals are highly polished and gave excel- 

 lent signals. The prism zone is occasionally striated, especially 

 the macropinacoid, though for the most part the zone is not 

 striated and each face is distinct and plane. The forms pres- 

 ent are : 



c = 001 



m = 110 



q = 114 



b = 010 



r] = 320 



/ = 113 



a = 100 



A. = 210 



V =112 



X = 130 



o = 011 



R — 223 



B = 370 



d = 102 



z - 111 



n — 120 



I = 104 



*N = 551 



N — 230 



v = 115 



y = 122 



The prism B = {3.70} occurs twice on two crystals as small 

 faces, usually giving a fair reflection. The angles measured 

 are as follows : 



28° 09', 27° 52', 27° 45', 27° 41' calc. 27° 45' 



The form was first noted by Diising* and classed as doubtful 

 by Dana and is not included in Goldschmidt's Winkeltabellen. 



*Zeitschr. f. Kryst. xiv, 481, 1888. 



