380 W. H. HOBBS 



Crystal form. — The crystal form of the lake diamonds fur- 

 nishes the most important method of comparing them. The 

 prevailing forms are the rhombic dodecahedron, the rhombic 

 dodecahedron with vicinal faces of a hexoctahedron, and a hex- 

 octahedron. The exceptions to the rule are found in the Sauk- 

 ville stone, a trisoctahedron ; the Burlington stone, a tetra- 

 hedron ; and the Milford stone, which from the newspaper 

 accounts would seem to be an octahedron. Twinning was 

 observed in one of the Plum Creek diamonds (in a hexocta- 

 hedron) and in the Burlington stone (in a tetrahedron). 



The crystals possessing dodecahedral and hexoctahedral 

 habits show, therefore, close affinities in their crystal forms, the 

 Eagle and Kohlsville stones, which are crystallographically almost 

 identical, being essentially intermediate between the Oregon 

 dodecahedron and the Plum Creek and Dowagiac hexocta- 

 hedrons. On all the crystals the faces are rounded, and unequal 

 development has produced distortion. The Eagle diamond 

 approaches nearer to the ideal form than any of the others which 

 I have examined. 



Surface. — Surface markings are common to most of the 

 stones. These are generally pittings, irregular in some cases, 

 but generally circular or triangular. On the Eagle stone there 

 are triangular elevations. 



Color. — The color of the diamonds in this region varies from 

 "white" to white tinged with green, and to pale yellow. The 

 stones of Milford and Saukville are "white." White stones with 

 faint grayish-green tinge (probably external) were found at 

 Oregon and Burlington, and one from Plum Creek ; while the 

 Eagle and Kohlsville stones and some of those from Plum Creek 

 are "Cape-white" (pale yellow). The several stones exhibit 

 also varying degrees of transparency, the Milford stone partic- 

 ularly being of a remarkably pure water. 



For purposes of comparison J;he most important facts regard- 

 ing the larger diamonds, have been brought together in the table 

 on the opposite page. 



