of Mineral Species of the Trimetric System. 51 
The angle of the vertical prism in Table III is near the angle 
of a regular octahedron (109° 28’). As this prism is a cleavage 
prism, and the only distinct one in the species, it appears to be 
the true vertical prism. 
But if we give the species another position, we may exhibit a 
relation to Sections II and III of Table II; and as they are all 
related to the species of those sections in composition, this rela- 
tion is of fundamental interest. Making the brachydome 12 the 
I: T=99° 52’; 10: 13=72° 58’; 1v: 11=82° 40’, 
which are almost identical with the angles in Orpiment. The 
following table presents the angles and axes of the species thus 
changed in position, and also those referred to on Table I. 














TABLE IIL A. 
Ba GAsl sce by EI ee De a ee 
i z. 1. ii. a bs &. 
ee 
Sulphur, 5+. +. 101°. 68 | 65°18’ | 76° 40’ | 15606: 1: 12342 
Marcasite, -.-.- - - 99° 40’. | 67° 12’ | 76° 24’ | 15049: 1: 1:1847 
IL 
Orpiment,- - - - - 100° 40’ | 73° g3° 30’ | 13511 :1: 12059 
Dimorphine (L) - - - {| 98° 6’ | 75°40’ | 83° 40’ | 1:2876: 1: 11625 
do, (IL) -.-. -| 100° 32’ | 74° 9’ | 84° 24’ | 18262: 1: 12030 
Mispickel,- - - - - 99° 52’ | 72°58’ | 82°40’ | 13520: 1: 1-1890 
| Aurotellurite, - - - | 101996" | 71°59’ | 83° 6 | 13797: 1: 12225 


It appears from the table that Marcasite, Fe 8’, is very near 
Sulphur in its angles and axes; while Aurotellurite (Ag, Au), Te?, 
and Mispickel, Fe(S,As)?, to which Leucopyrite, Fe As?, should 
be added, have the form nearly of Orpiment. It is a question, 
therefore, whether T'able III should not be suppressed, and the 
Species annexed to Sections II and Ill of Table II. The cleav- 
age constitutes the main reason for regarding the species as a sepa- 
rate Group. But notwithstanding the peculiarity in this respect, 
the affiliation with Sulphur and Orpiment is undoubted. — 
In Table IV. we recognize four sections : : 
I. Angle of macrodome near 70° 32’. 
Il. Angle of brachydome near 109° 28’. __ 
III. Angle of macrodome near 109° 28. 
IV. Angle of brachydome near 120°. 
The vertical axis in Section II is about one-fourth shorter 
than in Section I; in the latter 2i=85° 40’, which approaches 
li in the former, being very nearly the angle of Stephanite. 
i 
