MISCELLANEOUS COMPOUNDS. 63 



SPHALERITE (ZnS). 



(Cleavage piece, t= 1.53 mm.; transparent; slightly yellowish tinge. 



Curve a, fig. 50.) 



The transmission curve is marked for its extraordinary transparency 

 from 5 to 12 n, interrupted by slight depressions at 1.6, 11.2, and 13.2/4. 

 There is a wide band from 2.7 to 3.3/t, and complete opacity beyond 15/1. 



SILVER CHLORIDE (AgCl). 

 (Vitreous, t = o.8 mm. Curve b, fig. 50.) 



This is the only known substance for which no absorption bands have 

 yet been found in the infra-red. It seems to increase in transparency 

 with increase in wave-length, but is opaque for the "reststrahlen" at 53 

 and 6 1 p., as one would expect from its analogy to NaCl and KC1. 



56 7 B S IO II 12 13 /* IS 



Fio. 50, Sphalerite (a) ; Silver chloride. 



ORTHOCLASE (KAlSi 3 O 8 ). 

 (Yellowish tinge; subtransparent ; t = 0.07 mm. Curve a, fig. 51.) 



This mineral belongs to the feldspar group. It has bands at 2.85, 

 4.7, 5.7, and 6.28 p., which are bands of silicates. 



Curve c, t = 0.23 mm., is for a cleavage piece from a specimen of 

 unknown composition, and was simply marked "Feldspar." It has the 

 general outline of, but the bands are less marked than in, curve a. 



AMPHIBOLE (CaMg 3 (SiO 8 )i). 



(Silky gray color, probably tremolite; ground parallel to m; translucent; 

 # = 0.07 mm. Curve b, fig. 51.) 



This curve is similar to orthoclase, with bands at 2.8, 4.8, 6, 7.4, and 

 8.2 11. The 6 /A band may be the mean of the two found in orthoclase, 

 at 5.7 and 6.28 /*,, respectively. 



