Minerals from Terlimgua, Texas. 269 



compounds and the untenableness of the possibility suggested 

 by Professor Sachs. The question as to the structure of these 

 mercury-ammonium bodies, whether they belong to one or 

 other of the several types that have been suggested for them, 

 is outside the scope of this investigation. 



Montroydite. 



Orthorhombic-holoheclral, a : b : c= 0*6375 : 1 : 1-1977 

 (Schaller). Fifty-six forms observed, 45 new. Two crystal 

 habits with all intermediate gradations : (1) Prismatic, flexible, 

 dark red needles, commonly 1-J cm , occasionally 2|- cm long, by less 

 than l mm thick, often partially grayish from what appears to be 

 a thin coating ot some other ( presumably mercury ) mineral, or 

 minute and orange in several forms, notably wormlike and (2) 

 nearly equidimensional crystals of a few millimeters diameter. 

 The larger needles occur also in curiously twisted and curved 

 shapes, the minute orange ones in irregular rounded and loosely 

 coherent masses. There are also hollow, irregularly shaped 

 and bubble-like formations that in their interior resemble geodes, 

 being lined with or nearly tilled with one or both of the above 

 mentioned types of crystals. A somewhat different form of 

 bubble is found between large calcite crystals, smooth and 

 somewhat glistening exteriorly, gray-black and partially filled 

 with a spongy mass of crystalline material that is commonly 

 very dark in color. Precise descriptions of these and other 

 modes of occurrence are difficult to give in few words. 



Color, dark red to yellow-brown or orange-brown. Streak 

 yellow-brown. Transparent to translucent. Cleavage, perfect 

 1 010}. Hardness, 2-3, less than 2 (Moses). Brittle, also sec- 

 tile, but the long needles, extremely flexible, can be rolled 

 around a thin rod. Density not determined because of inability 

 to separate completely from free mercury enough for a satis- 

 factory test. 



Completely volatile without fusing, yielding in a closed tube 

 a sublimate of mercury only. Slowly blackened by hydrogen 

 sulphide, but not equally over all surfaces. 



Since the oxygen as given for montroydite by Professor 

 Moses was assumed by difference, a direct determination was 

 made by dissociating the mineral in vacuo, collecting, measur- 

 ing and testing the gas evolved. The result was to confirm the 

 identification of Professor Moses : 



Analysis of Montroydite. 



Theory Found in 

 HgO 0-2213 g. 



Hg 92-59 92-74 weighed as metal 



O 7*41 7'49 calculated from the volume. 



100-00 100-23 



