563 
1876 .] Mineralogy. 
however, been obtained with a black carbon worked to a knife edge : this 
stone is much harder than any other variety of diamond, the process of 
grinding to an edge occupying from five to ten days. Mr. Rogers’s investiga- 
tions have been the result of experiments undertaken for a different purpose. 
Failing to find a spider that would spin suitable web for the telescope of the 
meridian circle of Harvard College Observatory, an effort was made to produce 
upon glass lines of the desired quality and size. The objedt was accom- 
plished, and the investigations have been continued during a period of about 
three years. 
MINERALOGY. 
Dr. F. A. Genth has recently published a paper “ On Some American 
Vanadium Minerals.” He first mentions Roscoelite, a vanadium mica found 
by Dr. Blake, of San Francisco, California, named and called by him 
“ Roscoelite,” in honour of Professor Roscoe, whose important investigations 
have put vanadium in its proper place among the elements. Roscoelite occurs 
in small seams, varying in thickness from i-20th to i-ioth of an inch in a 
decomposed yellowish, brownish, or greenish rock. These seams are made 
up of small micaceous scales, sometimes \ of an inch in length, mostly 
smaller and frequently arranged in stellate or fan-shaped groups. They show 
an eminent basal cleavage ; soft ; the sp. gr. of the purest scales (showing 
less than 1 per cent, of impurities) was found to be 2*938 ; another specimen 
of less purity gave 2*921 ; lustre pearly, inclining to submetallic ; colour, dark 
clove-brown to greenish brown, sometimes dark brownish green. Before the 
blowpipe it fuses easily to a black glass, colouring the flame slightly pink. 
With salt of phosphorus gives a skeleton of silicic acid, a dark yellow bead 
on the oxidising flame, and emerald green bead in the reducing flame. Only 
slightly adted upon by acids, even by boiling concentrated sulphuric acid; 
but readily decomposed by dilute sulphuric acid, when heated in a seuled tube 
at a temperature of about 180° C., leaving the silicic acid in the form of white 
pearly scales, and yielding a deep bluish green solution. With sodic carbonate 
it fuses to a white mass. 
A remarkable deposit of tripolite, existing in the island of Barbadoes, where 
it is mixed with a certain quantity of carbonate of lime, has been examined 
by Dr. T. L. Phipson. Under the microscope it is found to be exceedingly 
rich in remains of fossil Infusoria, the forms of which are very well preserved. 
The silica is hydrated and soluble to a great extent in potash solution, and, 
like tripolite from other localities, it constitutes an excellent polishing material. 
On account of its value in this respedt tripolite has many imitations in com- 
merce, but it can be recognised at once by analysis, and also by the micro- 
scope. Among other useful purposes to which the Barbadoes tripolite has 
been applied latterly, we may mention that, having been found a bad conductor 
of heat, it has been used with advantage for covering boilers. 
In a paper on “ American Tellurium and Bismuth Minerals,” read before 
the American Philosophical Society at the meeting of August 21, 1874, Dr. 
Genth mentioned, on the authority of Mr. P. Knabe, a siskin green pulverulent 
mineral from the “ Iron Rod Mine,” Silver Star District, Montana, as a new 
“ Tellurate of lead and copper.” At that time he nad no opportunity of 
examining into the merits of this mineral. A qualitative examination proved 
it to be a hydrous vanadate of lead and copper and not a tellurate. 
The nickel ores of New Caledonia are found by M. J. Gamier to be not 
arsenio-sulphides like those hitherto utilised, but silicates of nickel and mag- 
nesia. The ore is found amidst the masses of serpentine very abundant in 
certain parts of the island, and associated with eupnotides, diorites, amphibo- 
lites, &c. The nickel is accompanied by iron, chrome, and cobalt ; these 
metals, especially the two former, are of an unexampled abundance. The 
cobalt is associated with manganese. These ores have also been examined 
by MM. P. Christofle and H. Bouilhet, who find that they belong to three 
distinct types — An emerald green hydrosilicate, compadt and hard, containing 
IS to 20 per cent of nickel and 5 per cent of water ; a yellowish green hydro- 
