Kunz and Washington — Forms of Arkansas Diamonds. 275 



Art. XXYII. — Note on the Forms of Arkansas Diamonds ; 

 by G. F. Kunz and H. S. "Washington. 



Diamonds have recently been discovered in the periclotite 

 stock of Mnrf reesboro, Pike County, Arkansas, the first having 

 been found Aug. 1st, 1906, and about 140 in all up to the date 

 of writing. A full description will be published later, but some 

 preliminary notes on the forms .and colors of the stones may 

 be of interest. 



The most commonly occurring forms are distorted hexocta- 

 hedrons, most frequently elongated, but occasionally flattened, 

 and with always- much rounded faces. The symbols of the 

 hexoctahedrons have not yet been determined, but more than 

 one form seems to occur, and in some cases they are merely 

 vicinal to the octahedral face. A flattened, trigonal, lenticular 

 form of spinel-twin, similar to fig. 4 in Dana's System (page 3), 

 is rather common, especially among the yellow stones. Another 

 form, also apparently twinned on 111, is shown by the largest 

 diamond yet found, which in form, color, and effect somewhat 

 resembles the well known " butterfly twins " of calcite from 

 Cumberland. It is crescentic in shape, flattened in one direc- 

 tion of the twinning plane and elongated obliquely to it on 

 either side. 



There are a few regular and undistorted octahedrons, which 

 show slightly rounded faces, though the center of these is 

 usually flat. The edges are often replaced by the dodecahedron, 

 and they are commonly further rounded by trigonal trisocta- 

 hedrons, with hexoctahedrons near the apices. The octohedral 

 faces are commonly marked by small, shallow, triangular pits, 

 which are most abundant toward the center ; while a few show 

 small, low, parallel ridges, the direction of which bisects the 

 face angle. ISTo cubes were seen, and tetrahexahedral and 

 dodecahedral forms seem to be equally rare, except as replac- 

 ing octahedral edges and angles. 



White stones are common, the white being exceptionally 

 pure and free from all tints of color, and usually absolutely 

 pellucid, like the so-called "river stones" of South Africa. 

 A considerable number are tinted brown or are a rich cinna- 

 mon-brown, while others are yellow, some of these being of a 

 pure lemon color. Some of the stones are gray, and a number 

 are very dark, almost black, bort ; but none of the hard, 

 amorphous carbonado seems to occur, though careful search 

 was made' for it, which should have revealed it had it been 

 present. 



The largest diamond weighs 6-| carats, and is 15 - 5 mm long, 

 7*75 high, and 4*2 thick, of an absolutely pure, pellucid white, 



