251 C. Pal ache — Miner ulogical JS T otes. 



being" larger, dark colored and deeply corroded, the later of 

 a pale pink color, small and with some of their planes still 

 brilliant. It was possible to measure these, and the forms 

 determined, as shown_ in the figure (fig. 3) were c (0001), 

 s y (1011), s(055l), and v (2181). The figure 



gives about the proportions of many of 

 these later crystals, which, being generally 

 attached by their sides to the older crys- 

 tals, were doubly terminated. Other crystals 

 show a broader base and greater relative 

 development of the form v, giving an equi- 

 dimensional habit, which is also, so far as 

 could be judged, the habit of the older 

 generation of crystals. In view of Schaller's* 

 study of siderite in which he questions the 

 accuracy of the accepted axial ratio, sev- 

 eral cleavage rhombohedrons which gave 

 brilliant and single images on the goniometer 

 were measured. The angle measured, 1011 

 to 1101 (average of six), was exactly 73°, 

 which agrees with the accepted value. It is of course recog- 

 nized that the considerable manganese content of this siderite 

 vitiates the comparison with Schaller's measurements made on 

 pure siderite, but the fundamental angles of siderite and rho- 

 dochrosite are identical according to Dana and replacement of 

 iron by manganese would therefore affect the angle but little. 



Sphalerite. — Sphalerite is sparingly present as light yellow 

 transparent grain and imperfect crystals too fragmentary to be 

 measured satisfactorily. 



Pyrite. — Pyrite is present only in minute amounts in crys- 

 tals showing cube and octahedron faces, implanted on siderite. 

 These crystals, which are exceedingly minute and somewhat 

 dull, present under the microscope an appearance quite unfamil- 

 iar for this mineral. The cube faces of each crystal are 

 divided into four equal areas by grooves running from a slight 

 prominence in the center of each face to the middle of each 

 edge. The appearance suggests interpenetration twinning, but 

 this could not be established by measurement. 



Quartz. — Quartz crystals of two tj^pes are found in the 

 cavity ; (1) simple combinations, m, r, z, with dull faces, 

 attached to the quartz of the cavity walls ; (2) fragments or 

 complete crystals imbedded in siderite. The second type is 

 glassy and contains chlorite inclusions. The crystals are pris- 

 matic in habit, often much distorted and highly complex in 

 development, as shown by the following forms found on the 

 two measured crystals: 



* Siderite and Barite from Maryland, this Journal, xxi, 364, 1906. 



