J. D. Dana’s Mineralogical Contributions. 217 
changing the lettering of the former. They represent crystals » 
of the species, seen in profile. A‘resemblance is apparent ata 
glance ; besides, f: f (over edge nm) of Euclase = 106°; I: I (over 
tt) Barytocalcite = 106° 54’. In Barytocalcite I,1 are cleavage 
plaues, and so also the plane O; and making I, I the sides of 
the fundamental prism and O, the base, the planes are as let- 
tered in the figure. The plane in Euclase corresponding to O 0 
Barytocalcite, would be ¢. Taking ¢ as O, and f for the com- 
parison as I, the axes of the two species are as follows: 
Euclase, I=106° a:b: c=0'83892 : 1: 182674 C=106° 8’ 
Barytocaleite, I=106° 54’ a:b: c=0-81035 : 1: 129583 C=88° 46’ 
In this view, r, u, i are the clinodiagonal prisms i, 3i, 47; the 
plane s =4-4, k=1-3, 9, a plane between s and k, mentioned 
by Brooke and Miller, is the plane 1, or belongs to the funda- 
mental octahedron, having for the angle X, 128° 48’. 
emembering how Auhydrite diverges from the other sulphates 
RS in angles and cleavage, and Wollastonite, another lime species 
from Augite in the same particulars, and also noting the differ- 
ence in angle between Tourmaline and Calcite, it will be admit- 
ted that the homceomorphism is close 
Since then, calcite and tourmaline are homa@omorphous, and 
also barytocalcite and euclase, tourmaline and euclase are mutual 
dimorphs as well as calcite and barytocalcite ; and, moreover, 
ourmaline and Calcite are isodimorphous. 
Hence the formula of Tourmaline, analogous with that of Eu- 
clase is the right one; and condensation in writing formulas is 
apparently the correct method, in place of the hypothetical sub- 
division adopted by Hermann, and others. i ld 
he Laurent School in France is obviously right in making 
the protoxyds and peroxyds replace one another, the parts equiv- 
alent being those having the same number of atoms of oxygen. 
The principle is sustained by the homeomorphism of Willemite 
and Phenacite, %n* Si and BeSi; or if Be be written Be’, other 
cases show the mutual replacement of Be® and 1 It is exempli- 
fied in Augite and Spodumene, the former 2? Si, the latter (R’, #)Si*; 
and also in many other species. 
15. Observations on the formulas and relations of some species. 
_ Luclase, Datholite, and Sphene.—The formulas are as follows, 
M accordance with the above principles. 
i ie ee £ 
lase, . 3 i : (4414-38e) Si? =‘%) Si 
Datholite, adopting th iew, and making 3H Mie ws 
replace eerie anor desory, haethe eeacds, - (¢R44B) Si =k, B) om 
Or if 8H replace 80a, it becomes, - - (@R*+4B) Stas, B)8i 
| 4 - * a - . (€a+Ti) Sita sit 
Szconp Szares, Vol. XVII, No. 50.—March, 1854. - 98 
