224 J. D. Dana on the Isomorphism and 
VIIL ANATASE, Ti~HORN QUICKSILVER, Hg Cl. 
A pyramid in Horn quicksilver has the basal angle 136° ; and 
the corresponding angle of anatase is 136° 22’. 
IX. SULPHUR, 8, and SCORODITE, #e As+4¥f. 
The axes of sulphur are 19043: 1:0°8108; and those of Sco- 
rodite 0°9539: 1: 0°8527. The vertical axis of sulphur is hence 
double that of ecw (2 x0-9539=1-9078), while the other 
axes are nearly equal. (The planes of the vertical rhombic prism 
common on crystals of scorodite, belong to the form «P2.) 
X. CELESTINE, Sr S—WHITE IRON Eke Fe S2—GRAPHIO TEL- 
URIUM, Ag Te+2Au 
The angle M: M of Celestine is pre a White Iron Pyrites 
106° 2’; a brachydiagonal prism of the former has the side angle 
103° 58’ ; ; of the latter 99° 58’. Graphic Tellurium has M:M 
= 107° 44’; a macrodiagonal prism in Celestine is 101° ss in 
Graphic Tellurium 103°. 
XI. CHROMATE OF LEAD, Pb Gr—MONAZITE, (Ge, Th, La)3 6. 
The forms are monoclinic. In Chromate of Lead, M:M =93° 40’ 
and P:M=99° 11’. In Monazite, M: M= 93° 10’ and P: M= 100° 
— 100° 25’. The forms of the crystals are similar in the occur- 
ring secondary planes.—Compare figure 2 of Chromate of Lea 
in the author’s Mineralogy* with 2 of Monazite in the same 
work ;+ og general form is similar; and the planes M, é, €, 4, €, 
a, a’, ary eres P, - Pa, aP’ a, P’ x, 2P’ x) are the ne ip 
the two. €:é in the former is 1199, i in the latter 119° 22’; 
in a former is 107° 40’, in the latter 106° 36’. 
XIL BERYL, Be Sit+-241 Siz, or a = +1 Siz—NEPHELINE, R2 si 
+24 
em 
=f q 
In Nepheline, P on two fii on the basal edges is 134° 3 
and 154° 27’; in beryl, the corresponding angles are 130° 59’ 
and 150° 6’. 'The vertical axis of nepheline is 0:4629, of beryl 
0-4993. These species are only approximately isomorphous. 
The axis of quartz is a little more than double that of beryl, 
it being 1-0996 and 2 x 0-4993 =0-9996. 
We mention also, without particular remark, some of the ad- 
mitted cases of isomorphism, among species that are alike in gen- 
eral constitution but different in atomic proportions. 
1, Pyroxene, Acmite, Hornblende and varieties. 
2. Scapolite, Meionite, Wernerite, Dipyre, Gehleni 
3. Tale, containing magnesia and silica in different vioriitanil 
ae 
4, pl. x, Mohs’s itr des Min., 
alee + Alo Ses copies Jour. fig. 1, but with different reset and the 
in: Dukoney’> Se BT vol. iv, pl. 228, fig. 476 
