294 W. H. Melville — Metacinnabarite from, California. 



represented in fig. 1, and actually occur on one crystal with 

 equal regularity. Fig. 2 is the combination of x(lll) with the 

 plains of the antilogue pole tabulated above. The distances of 

 the poles of all the rhombohedral faces from the pole of (111) 

 were measured on the same crystals and no doubt can possibly 

 exist as to the system of crystallization. Viewed as they are 

 implanted on the rock, the crystals present much similarity to 

 tetrahedrons, but examination shows that the face of the nega- 

 tive rhombohedron in combination with the basal plane forms 

 an isosceles and not an equilateral triangle. Beside_s_ the 

 measured angle /3 = 82° 45' the plane acute angle of (33, 17, 17) 

 = 11° 29' 40" was calculated from the fundamental angles. 

 The crystals vary in length from l*24 mm to 2 - 3 mm and in width 

 from - 59 mm to 0*97 mm ; possess a high metallic luster, black 

 color, black streak with slight reddish tinge ; are brittle with 

 hardness about 2 ; and give the reactions for zinc and sulphide 

 of mercury. 



This mineral I consider metacinnabarite since the atomic 

 ratios give a very improbable formula. Its specific gravity is 

 much below that given to the species by Mr. G. E. Moore* 

 7 '70 — 7'75 for the reasons stated above. On the other hand its 

 somewhat close resemblance to guadalcazaritef in chemical 

 and physical properties — for Castillo mentions rhombohedral 

 crystals of this mineral — might point to its identity with this 

 species. But it must be acknowledged to be metacinnabarite 

 in composition with a small percentage of impurity of other 

 sulphides such as would be naturally expected on precipitation 

 and crystallization from solution. Again the crystals of 

 metacinnabarite, many of which I have examined from local- 

 ities in California as far back as 1882, are very indefinite and 

 although they appear to be rough cubo -octahedrons, might 

 really consist of the combination of basal plane and rhombo- 

 hedron. Mr. S. L. Penfield^: has described metacinnabarite 

 crystals from California, and determines them to be hemihe- 

 dral isometric forms. One measurement is there given, viz : 

 322/s32_2_=86° 54J / _(mean of three) which approximates the 

 angle (111) ^(33, 17, 17) = 85° 50', the supplement of which 

 appears in the table above. It is possible that these two planes 

 may form the combination I have indicated. ~No angle occurs 

 on crystals in my possession near that of 211 ^112=33° 15' to 

 36° 54 7 which Mr. Penfield found. It is barely probable that 

 metacinnabarite is dimorphous. If it should happen that bril- 

 liant crystals of metacinnabarite from the Knoxville quick- 

 silver district should be found, I firmly believe that their habit 



* Dana's Mineralogy, App. I, 10. f Ibid, App. IT, 25. 



% This Journal, June, 1885, p. 452. 



