: E S. Dana—Orystal af Andalusite from Delaware Co., Pa. 478 
Art. LVIL—Ona crystal of Andalusite, from Delaware Co., Pa. ; 
by Epwarp S. Dana. 
THE annexed figures represent a remarkable crystal of anda- 
lusite, from Upper Providence, Delaware Co., Penn., received 
by Professor Dana from Dr. George Smith, and now in the Yale 
College Cabinet. Figure 1 shows the crystal (natural size) with 
the planes as actually 
occurring. It will be ath: 
noticed that while all 9 rt 
the known planes, “| | 
with one exception ed 
~ Tye} 
(22), are present, there 
is an irregularity in 
their occurrence al- | 
most amounting to a f 
kind of hemihedrism; 
li and 72 app but 
once, instead of twice, | 
} 
| 
i 
| 
| 
} 
and 72, 22, and 1 once, 
instead of four times. 
Figure 2 shows the 
crystal in its theoretical form, with all the planes as they would 
regularly occur. Za gave 88° 15’ (that is, 91° 45’), and O 
the macrodiagonal section the angle 93° to 94°; this obliquity, 
however, is not in the right direction to explain the partial 
hemihedrism. 
t 
small, and there was nothing in their manner of occurrence to 
Suggest that the peculiarity of the crystal figured was anything 
more than an accidental irregularity. In all of these speci- 
mens there was a great diversity in the prismatic angle, and 
obliquity in the angle of O upon the diagonal sections was very 
common. 
A word should also be added-in regard to the cleavage in the 
Specimens from Delaware Co. In most cases it was irregular, 
many of the crystals having a fibrous, tremolitic structure, and 
in others it was radiated. The regular cleavage parallel to the 
prismatic faces, howeyer, did occur, and a chemical analy . 
several of the specimens is needed to determine whether in the 
former case any change in constitution had taken place. 
Am. Jour. 7 Series, Vou. IV, No. 24.—Dzc., 1872. 
