DEc., 1908. MINERALOGICAL NOTES 161 
usually give successive signals. Fig. 1, Pl. LI, exhibits the usual 
development. In addition it may be noted that one individual of 
the twin usually shows a tendency to grow by the other, suggesting 
a penetration twin; but the growth is never extended far. Deter- 
mination of the specific gravity gave 4.284 The forms and measure- 
ments observed are as follows: 
h (210) é (ror) 
Observed Calculated 
fees == (270) A (120) AG SOs 2% elie ae 
eye =". (210) ‘A. (210) — eae anon rege i 
fees = (101) ‘A (lor) — Wi meta Ac de 
e@ A e oftwin = by bali eit RATA! 
SRA bene 
TUCKAHOE, MISSOURI 
As is well known; sphalerite occurs in the Joplin district in the 
form of small crystals in clay, and occasionally in sufficient abundance 
to be used as an ore. Mr. James Roach of Tuckahoe, Missouri, who 
mines ore of this character, kindly selected about 25 of the best crystals 
and presented them to the Museum, Mus. No. M 6382. The crystals 
are of interest as showing an unusual habit for sphalerite and one 
which is in some respects difficult of interpretation. The crystals 
range from 5 to 20 mm. in diameter and are of a generally 
tetrahedral form. In color some, generally the smaller ones, are 
reddish-brown and nearly transparent, but the majority are dark- 
colored and opaque. The development of the crystal planes varies 
from almost indiscriminate rounding to well-defined. All the crystals 
_ however, as stated, show a general tetrahedral form. Now and then 
apparent re-entrant angles are to be seen, which suggest that the 
crystals are probably twins; but on breaking the crystals,no differ- 
ences of cleavage can be observed to confirm this supposition. Asa 
rule the crystals are made up of only fifteen planes, but occasionally 
eighteen can be observed. None of the planes are sufficiently brilliant 
to give measurements with the reflecting goniometer, but the crystals 
are of such size that satisfactory results can be obtained with the 
contact goniometer. By study of the crystals in this manner the 
presence of the tetrahedron and cube can be definitely and satisfac- 
torily determined. These forms are always present in their full num- 
