LARSEN AND STEIGER: MINERALOGIC NOTES 9 



which are very low in magnesia and iron, and the chlorite and 

 other minerals are largely vein fillings rather than replacements. 



The chlorite is green in color and is soft and friable. It is 

 fibrous to platy and is finely crystalline. 



An optical study of the chlorite from various parts of the 

 Creede district shows that it varies somewhat in its optical 

 properties and no doubt also in chemical composition. The 

 material analyzed from the Last Chance mine on the Amethyst 

 vein is in very minute interwoven fibers of positive elongation 

 and optically negative character. The axial angle is moderate. 

 The mineral is pleochroic: dark green parallel to the fibers 

 (/3 and 7) and nearly colorless normal thereto (a). The mean 

 index of refraction is about 1.637 =*= 0.005 and the birefrin- 

 gence is about 0.01. The fibers are too small for a satisfactory 

 optical study. A specimen of the mineral from the Park Regent 

 mine, also on the Amethyst vein, showed essentially the same 

 optical properties, but the indices of refraction are slightly 

 higher (n = 1.643). A specimen from the Amethyst mine 

 gave = 1.638 =*= 0.003. 



A specimen from the Ridge mine is considerably paler in color, 

 is less strongly pleochroic, is a little more coarsely crystalline, 

 and has lower indices of refraction, but is otherwise similar. 

 It is optically negative and has a moderate axial angle. X is 

 normal to the fibers and plates and is very pale green; Z and Y 

 are a somewhat darker olive-green. The refractive indices are: 

 a = 1.595 ± 0.005, 7 = 1.605 ± 0.005. Another specimen from 

 the Ridge mine consists of very minute fibers and has a mean 

 index of refraction of about 1.585 ± 0.005. A specimen from 

 the Solomon mine is similar but its mean index of refraction is 

 1.617 ± 0.005. 



These data indicate a moderate range in the composition of 

 the chlorite. The mineral from the Ridge-Solomon vein with 

 its lower index of refraction is probably higher in A1 2 3 and 

 lower in Fe 2 3 and higher in MgOand lower in FeO. It ap- 

 proaches aphrosiderite or delessite in composition. The analysis 

 of the gouge from the Solomon mine (analysis 4, table 2), which 

 was made up largely of chlorite but contained some quartz and 



