DEc., 1908. MINERALOGICAL NOTES I4I 
ments were made by contact. The forms determined and measure- 
ments obtained are as follows: 
r(rolr1)+R B:(5161) + 4R3 A (2352)—4R5 
(5491)+ Ro G:(7295)+R2 
J 2(5273)+R¥ 2(1235)—ER3 
Observed Calculated 
eee = (2352) A. (2532) = Asad Lea 2ST | 
Pee eee (TOE) | (2352) = 36° Aaa aes 
vu A pl = (5491) A (5941) = 66° Gus heey 
ree. a (S161) A -(156T) = 136° ech HO 
eee = (r0l1) © A (5163) = Ee a ie ¥ 
B AB = (1235) A (1325) = Be octal 0 
pee — «= (7295) A, (9275) = 21° 20° 44’ 
feeds = (olrr) A. (7925) = faphicley Vy Vee eas 
Yat ie eer toli) ~ Cs49r) eh We AAs 7 iat Gi 
oe) = © (olrz) A. (8273) == 98° ‘ators meee 
A calcite twin bearing the Museum No. M 8692 is shown in Fig. 1, 
Pl, XUVIII. This is from the Crystal Palace mine, Central City, Mis- 
souri. The twinning plane is ¢ (oo01). The dominant forms are the 
rare rhombohedron v.(0553) and e (o1l2). These produce an approxi- 
mately spheroidal twin, but only about half the spheroid is present in 
this specimen. The halving is due to the manner of growth from the 
attachment. The twin is complete in a polar direction, but incom- 
plete equatorially. The length of the polar diameter is 5.5 cm. 
The substance of the twin is wine-yellow, and transparent. All of 
the planes, however, with the exception of those of the rhombo- 
hedron e (o112), are coated with a thin, firmly adhering layer of iron 
oxide, chocolate brown in color. The planes of e are striated, as 
represented in the drawing, and as also represented there unite with 
those of v- by a curved edge. The common forms v and M modify 
the dominant forms. The twin is thus made up of three rhombo- 
hedrons, two of which are negative and one positive, and the scale- 
nohedron v. Of the rhombohedrons, v- (0553) seems to have been 
first noted by Thtrling * who, however, gave it no letter. Whitlock,+ 
who observed it on calcite from West Paterson, N. J., gave it the 
letter here employed. 
The measurements which were made on the specimen were 
by contact, but the planes were so well marked that there seems 
* Neues Jb. Beil. Bd., 1886, 4, p. 380. 
t Am. Jour. Sci., 1907, (4), 24, p. 427. 
