Mineralogy and Geology. A19 
Figure 11, Idocrase. Froma crystal from Sanford, Maine, furnished 
the author by L. Stadtmuller. It is nearly half an inch in diameter, 
and the faces are all bright. e Idocrase occurs massive or sub- 
columnar at that place, and there are often cavities of fine crystals. 
The crystals are sometimes thinly sprinkled over with dark green crys- 
tals of pyroxene, hardly a line long, which are loosely attached to the 
idocrase and are evidently of subsequent origin, apparently a result of 
its alteration. The crystals of idocrase undergo ready alteration, os 
often the surface peals off in layers, over the whole summit; an 
alteration has proceeded inward with such exactness that the ie 
layer leaves behind the same number of small secondary planes as in 
the complete crystal, and all equally brilliant in polish. This is the 
more wonderful since there are no cleavages parallel to all or any of 
these small secondary planes. it color of the idocrase is brown and 
greenish-brown. In one specim n having a columnar structure, the 
columns along a straight line i vanolien in length met at an angle of 
56° to 60°, indicating composition parallel probably to the plane 4i. 
Figure 12, Albite from the Middletown feldspar quarry. The crys- 
tals are half to one inch long, and in part transparent. They are mostly 
in twins parallel to é, but so united that the plane O and 1? are in the 
same plane nearly. From one crystal the author obtained for O: ii, 
2 20. 
o., N, Y., ¢ a falfiipat shown by Smith and Brush to. bei rthoclase 
_ Figure 14. Topaz from Trumbull, Ct. The crystal is transparent 
and a fourth of an inch in diameter. The most of the terminal planes 
h. 
a Pigerea 15,16, 17, Tourmaline. Figure 15 represents an upper 
view of the termination of a slender transparent crystal of a light yel- 
lowish color, from London hae near Unionville, Pennsylvania. lt 
is from the cabinet of T. F. Seal, of Unionville. Figure 16 is froma . 
black crystal one inch in fons ‘from Northern New York. Fig. 17 
is a brown tourmaline from Canada, menor? from T. 8. Hunt of the 
Geological Commission, Canada. e rhombohedron of 103°, 
Figure 18, Apophyllite from the cli mine, Lake Superior region, 
Michigan. The crystals are from one-fourth to half an inch in ap th 
and transparent. The ey are generally tabular, but occasionally oc 
— The plane 73 is not the prism usually noted on crystals of this 
specie 
tal from Cheshite, Conn. ; figure 20, one ite the Bldrid e gold mine, 
Buckingham Co., Va., sent the author b The size 
varies between n one: -fourth and tice: earth of aninch. All the planes 
but the striated vertical planes are highly polished. The terminal face 
is often cavernous, the polished plane O being often finished at differ- 
ent elevations nes t of the actual summit of the crystal. 
Figures 21, 22, 23, Baigieniee; from different reap from the 
eet 
tor, C. M. Wheatley. The crystals pani the same ae anes nearly, 
but are elongated in differ te avian They are brilliant, glassy, 
often h. 
n transparent, and sopmemarice inch or more in lengt 
