84 J. D. Dana’s Mineralogical Contributions. 
light. ee thus afforded the angles O: R=119° (to 119° 55’) 
O:2R=105° 30’. These angles correspond to R: R=82° 15, 
and axis @ seen 527. 
6. Crystallization of EZ. Oe as nd its Homeomorphism 
ith Wollasto 
Messrs. Smith and Br ee have ee eu that the distinctly 
crystallized Lancasterite is PAY ASRIDAE NEN while the pearly 
foliated mineral called by this name, is Brucite. The crystalliza- 
tions from Texas, Pennsylvania, (Low’s, oA 
also Wood’s mine,) are either massive fibrous, 
and radiated, looking much like Thomsonite, or 
attened or acicular crystals, more or less group- 
ed. At Hoboken the same mineral is found in 
very fine acicular crystals clustered together 
and having the aspect of natrolite. ‘The lustre 
is vitreous. ‘A distinct cleavage has not yet been 
observed. ‘I'he ‘Texas crystals occasionally 
have regular terminations, as may be seen with 
a maguifier of some power. They belong to 
the monoclinic system. With the reflective 
goniometer as above, I found for the angles 7: 23 = 112—1133°; 
ii (back) : -22 = 103°; 22: ~22 (adjacent in same pyramid) = 1433 
—145°; opposite orthodiagonal edges of the pyramid (or y on y) 
over the summit =94° ; same edge on orthodiagonal edge of prism 
(yont) 133°. The last two angles were measured with Smith’s 
goniometer attached to a compound microscope. 
These measurements give for the inclination of the vertical 
axis, 82—83°; for the angle of the’ rhombic prism 72 (or « 
corresponding ‘eB the octahedron 23, 51° 26’ to 51° 32’; for the 
vertical axis, ar ay orthodiagonal of the octahedron 
2a: 20 C= 1 tm awk Ut. : 
The prism 7 (or xP), ietiee would have the angle 87° 52’-88°9 ; 
and taking this as the fundamental prism, then the pyramid will be 
formed of the planes 22 and —22, (2P/2 and oe as represented 
in the figure. We shall also have 2t: 21 (2P! ©: 2P’ wc) = g4° 
O:2i(0P: 2P’ )=137°, i: 2i( cP’ »:2P’a a 133°. 
The angle of the aa (J on £) is nearly the angle of Wollas- 
— (this J our. [2], xv, 449), and moreover O:2i in Wollas- 
tonite is 137° 48’, or but 49 Seton from that of hydromagnesite. 
Wellanosite and hydromagnesite are hence obviously ho- 
meeomorphous. ‘To this homaomorphous group belong, as else- 
where shown, 
~ 
ee 
Borax, . -.. 3 RDA Pyroxene, . ‘ R Si? 
Glauber salt, . | NaSHve Acmite, Na Si4+PeS? 
Hornblende, . R:Si* Spodumene, Re B244Ks Siz, or (R*, B) Si? 
and probably Laumonite, Ca* Si? +41 Si?--18H, which is, a Spodumene with 18 
