Palache and Wood — Crystallogra/phic Study of Millerite. 353 



Rhomb ohedrons. 



These are the chief terminating faces whether they occur as 

 cleavage or as crystal planes. The faces, when crystal planes, 

 are not very bright, although the markings and roughnesses 

 which make them dull are never well characterized. 



r, (1011). The unit rhombohedron was found on all but 

 two of the measured crystals. In a very few instances it was 

 certainly cleavage ; and in a few cases it was impossible to say 

 whether cleavage or natural growth had produced the facet. 

 It was developed in relatively large and perfect facets, con- 

 stituting the dominant terminating form. While not always 

 of good reflecting quality, the faces were usually definite and 

 exhibited no definite markings. 



p, (0221). Next to r the new rhombohedron p is best 

 developed as a termination. It is not found as cleavage. It 

 occurs in rather large faces of dull reflecting power for the 

 most part. It is missing from nine crystals only out of the 

 twenty-eight measured, occurring, therefore, with less fre- 

 quency than r. No definite markings were seen on its faces. 

 The observations on which it is based are stated in summary 

 form on_p. 349. 



v, (5052). This rhombohedron, noted by Miller in his first 

 paper, but omitted from his Mineralogy, occurs on five of the 

 crystals, three of them, singly terminated, showing two faces 

 each. The measurements on which the form is based follow. 



Crystal. Signal. , Headings. ^ 



16 good 



16 good 



1 8 very good 



20 poor 



20 good 



21 fair 



2 1 good 



24 fail- 

 Average very good to fair 

 Calculated 



Scalenohedrons. 



These forms are entirely new to millerite. They are pres- 

 ent on the Orford mineral as small but distinct facets on over 

 half the crystals measured. The faces are fairly bright, yield- 

 ing good images, and for the most part they are not pitted or 

 striated ._ 



s, (2131). This scalenohedron occurs on two singly termi- 

 nated crystals, in one case five of its faces being present. The 

 measurements which establish it are given below. 



* ©i is the value of (j> referred to the first sextant on the right, that is, the 

 difference between $ and the nearest multiple of 60°. 



Am. Jour. Sci.— Fourth Series, Yol. XY1II. No. 107. — November, 1904. ' 

 24 









4 



»i* 



i 







29° 



39' 



29° 



39' 



44° 



03' 



149° 



41' 



29° 



41' 



43° 



57' 



149° 



19' 



29° 



19' 



43 c 



23' 



30° 



42' 



30° 



42' 



43° 



33' 



150° 



07' 



30° 



07' 



43° 



25' 



29° 



52' 



29° 



52' 



43° 



24' 



150° 



10' 



30° 



10' 



43° 



25' 



89° 



31' 



29° 



31' 



43° 



51' 







29° 



53' 



43° 



39' 







30° 



00' 



43° 



23'' 



