486 B ratiner — Minerals Associated loith Diamonds and 



The corundum reported is of the ruby and sapphire varie- 

 ties, and is of a pale gray color. 



The magnetite is sometimes found partly altered to hematite 

 and the large amount of hematite and martite found with the 

 diamonds is to be referred to this source. 



Metallic copper was found in several of the samples, but as 

 the pieces are very small, and invariably curled up like filings, 

 it is supposed that they came from the pieces of sheet copper 

 often nailed in the bottom of the bateas to mend holes, and that 

 these small fragments have been scratched off by the gravels 

 while the washing was going on. 



Dr. A. F. Rogers gives me the following note upon the 

 favas and diamonds found in these concentrates: 



" The phosphate ' favas' are rounded grains with faint greasy 

 luster and pitted surfaces. The colors are quite variable, faint 

 yellow, bluish gray, and dark brown. Under the microscope 

 fragments are almost opaque, with a faint action on polarized 

 light and have an aggregate structure. The index of refraction 

 is about l - 62 and the hardness about 5. In composition the 

 'favas' are hydrous phosphates of aluminum. They probably 

 vary in composition as they do in specific gravity, some being 

 a little greater than 3*3, and some a little less. 



u Diamonds were found in two samples, — a single smoky 

 cleavage in one sand, and thirty-five crystals and cleavages in 

 another sample. These crystals are colorless, yellowish, green- 

 ish, and pale wine-colored. The crystals are the common iso- 

 metric forms, usually octahedral in habit, the faces being the 

 octahedron, the dodecahedron, and the trisoctahedron. Some 

 crystals are fairly sharp octahedrons with plane faces and 

 grooved edges, but most of them have curved faces in oscilla- 

 tory combination with each other. Several spinel twins of tri- 

 angular shape were noticed. The crystals vary in size from 1 

 to 2" ,m in diameter. One carbonado was found in this sample." 



Four microscopic slides have been made from the diamond- 

 bearing quartzites collected south of Leneoes for the purpose 

 of ascertaining whether any of the minerals that are so charac- 

 teristic of the metamorphic rocks occur in them in such manner 

 as to show that they originated in the quartzites themselves. 



Unfortunately the only minerals thus far found in the micro- 

 scopic slides are quartz, chalcedony, and tourmaline : quartz 

 forms the mass of the rock, the cementing material is partly 

 quartz but largely chalcedony, while the tourmaline appears to 

 have been carried in solution into small irregular cavitie6 and 

 there crystallized out. The dark greenish bands made by the 

 tourmaline are quite visible to the naked eye in hand speci- 

 mens. This particular microscopic examination does not, there- 

 fore, throw any positive light on the subject. But in view of 

 the scarcity of the diagnostic minerals, no other result was to 

 have been expected from the examination of so few slides. 



