260 HUlt brand and Schaller — Mercer;/ 



are deposited on a matrix of two kinds, first a soft siliceous- 

 aluminous, earthy mass, sometimes gray but usually of a pink- 

 ish color and containing a small amount of calcium carbonate, 

 and second, a fairly pure layer of calcite with large scalenohe- 

 dral crystals projecting from the surface. The general 

 associations of the several minerals are given below, but there 

 are many exceptions that will be noted in the full report. 

 Kleinite is found with gypsum, calcite, seldom with barite and 

 calomel, either loose or on a whitish clayey gangue, only once 

 or twice accompanied by terlinguaite ; calomel with calcite, 

 mercury and eglestonite on the pinkish earthy gangue ; egles- 

 tonite with calomel, calcite and mercury on the pink gangue or 

 on calomel ; montroydite with calcite, terlinguaite, and mer- 

 cury on the calcite layer ; terlinguaite with calcite, montroy- 

 dite and mercury on the calcite layer. 



Several members of this group of minerals are characterized 

 by a most unusual property, namely, proneness to change color 

 rapidly on exposure to light. With respect to terlinguaite 

 and eglestonite this change is of a permanent character and the 

 result is to impart to the minerals an appearance often quite 

 different from that they originally possessed. With kleinite 

 the change is not to a different color but onky to a different 

 shade, and it persists only as long as the exposure itself, the 

 original color returning in the dark. From published and 

 privately communicated statements it would seem as if these 

 minerals, in their earthy forms at least, must be difficult to 

 distinguish as a rule when first found, by reason of the simi- 

 larity of their original colors, all more or less pronouncedly 

 yellow. 



In addition to the specimens first received from Mr. Turner 

 many fine ones were donated by Mr. J. H. Hartley, who was 

 also connected with one of the Terlingua mining companies, 

 and later Mr. R. M. Wilke, of Berkeley, California, gave kleinite 

 when more was needed. All was, so far as known to us, from 

 the properties of the Marfa and Mariposa Mining Co., and 

 chiefly from the Terceiro shaft. Professor A. J. Moses kindly 

 identified the new mineral with his No. 5 and sent us his orig- 

 inal measurements of the latter. To these gentlemen, espe- 

 ally to Mr. Hartley for his most generous liberality, also to Dr. 

 P. Gr. Nutting of the Standards Bureau and Prof. B. B. Bolt- 

 wood of New Haven, who kindly made certain tests, we take 

 occasion to express our deep sense of obligation. 



In the several descriptions that follow we have incorporated 



data already correctly given by Professors Moses and Sachs,* 



as well as the new matter gathered by ourselves, in order to 



present as complete a record as possible of the minerals 



*Sitzb. K. Preuss. Akad. Wiss., 1905, 1091-1094. 



