364 . On the Geological Associations of Tellurium. 
Ouro Preto, the capital of Minas Geraés, in Brazil. The rock in 
the neighbourhood is a thin-bedded slate, usually talcose, and 
frequently containing chlorite also. The vein, which ranges through 
both mines, and is traced far beyond them on the line of its course, 
bears about E. and W. (magnetic), and is from twenty to forty feet 
in width. Its chief ingredients are hard milk-white quartz and 
quartzose slate. ‘Though nowhere rich in gold, it is rarely desti- 
tute of it; the precious metal—sometimes in crystalline grains, the 
tellurium, and minute crystals of iron pyrites, sprinkling thinly, but 
tolerably regularly, the whole mass of the vein. There are, how- 
ever, quartzose portions in which the tellurium occurs in large masses, 
presenting a confusedly crystalline structure, and sometimes long 
spiculee of it are inclosed in translucent quartz. 
During the summer of 1852, I visited—besides other parts of 
the United States—Spotsylvania county, near Fredericksburg, in 
Virginia. The Whitehall mine in that district is wrought in a 
deep blue clay slate. The lodes bear about S.E. and N.W. (mag- 
netic), and are of considerable size; their principal constituent is a 
hard white quartz, sometimes marked with ferruginous stains, and 
occasionally they contain large masses of slaty matter. The gold, 
for which the mine was wrought, is for the most part scantily, but 
pretty uniformly scattered through the whole body of iron-tinged 
parts than elsewhere ; where the quartz is somewhat drusy, it has 
occasionally a tendency to crystalline structure. The tellurium is, 
like the gold, only more scantily, dispersed through the quartzose 
matter ; but no crystals of it have yet been discovered. 
Distant as Minas Geraés and Virginia are from each other, the 
gold of the Morro de Sao Vicente neighbourhood has considerable 
resemblance to that of the Fredericksburg district ; both, although 
of the very best quality, having an exceedingly slight tinge of green. 
Whether this hue may be from a minute portion of tellurium being 
naturally alloyed with the gold; or whether the two metals, being 
stamped together, are imperfectly separated by dressing, and form, 
when smelted together, an artificial combination, I am unable to say. 
No other natural union, however, if this be one, has yet been de- 
tected in either of these districts 
The sulphurets of antimony and of bismuth occur in the gold 
vein of Catta Branca, near Morro de Sao Vicente; iron pyrites and 
blende are mixed with the gold and tellurium of Paciencia; and 
galena is in like manner associated with them in many of the mines 
near Fredericksburg. 
The engrossing occupations which have led me into these distant 
tracts, have not permitted me to search for the combinations of gold 
and tellurium ; a reward probably reserved for some future inquirer 
better qualified for the task than I am, and with leisure for the 
pursuit, which I have not enjoyed. 
3 CLARENCE PLACE, PENZANCE, 
September 19, 1854, 
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