the Arseniates of Copper, and of Iron. 189 
really contains. The natural decomposition of this arseniate, 
which produces an oxide of iron of a fine reddish yellow 
colour, strongly confirms the result of Mr. Chenevix’s 
analysis. 
Gmelin, in his Principles of Mineralogy, printed at Gottin- 
gen, in the year 1790, had already supposed that these crys- 
tals could not belong to the substance which, in mineralogical 
publications, had been -called arsenical copper ore. He had, 
consequently separated them, leaving them, however, among 
the ores of copper, under the name of wiirfel ertz. 
The double combination of the arsenic acid with iron and 
copper, although it had appeared to exist in the arseniate just 
spoken of, in the mines of Tincroft and Carrarach, had not 
excited the attention of mineralogists. It is however possible, 
that the transparency, the brilliancy, and the pale blue colour 
of its crystals, might occasion them to be mistaken for crystals 
of a stony nature. Besides, their smallness might easily cause 
them to escape the notice of common observation, particularly 
when they are not in pretty large groups. 
The matrix of these two arseniates is exactly the same as 
that of the arseniates of copper ; consisting, like that, of quartz, 
mixed with yellow, grey, and vitreous ores of copper, with 
oxides of iron, and with mispickel. The mines of Huel Gor- 
iand and Muttrell, although not situated in the district of the 
tin mines, have yet produced some specimens of tin, the crys- 
tals of which are covered with those of the arseniate here 
spoken of. Two specimens of this kind are in the collection 
of Sir John St. Aubyn. 
