On the Artificial Formation of Minerals. 297 
‘2 dually, and without passing through any shades of green or 
blue. 
The results of these experiments, therefore, show that 
phosphate of iron is capable of producing, in combination 
with alumina especially, but likewise with other substances, 
a series of colours of which the intermediate phase is pure 
blue; on the one side the dark violet seen in some varieties 
of fluorite, and on the other the bluish-green of the Arendal 
apatite. In some instances these colours may pass, by a 
Subsequent oxidation, into yellow and red shades, like those 
‘so frequently observed in cyanite. 
The fact that the largest and most perfectly developed 
crystalline minerals occur either in druses or upon lodes, has 
been brought forward by Bischof as evidence in favour of 
their production through the agency of water. His whole 
argument, however, ends in establishing, by general reason- 
ing from physical and chemical principles and circumstantial 
evidence, a probable hypothesis, in place of vague and often 
contradictory opinions hitherto entertained. As yet the hy- 
pothesis is destitute of any such positive experimental evi- 
dence as would justify its reception as an adequate theory of 
mineral development and alteration. 
The argument for the aqueous origin of minerals derived 
from the presence of constitution water in minerals, zeolites, 
&c., has recently been met by direct experimental facts,* 
which, at least, destroy that portion of it that is intended to 
prove the impossibility of their formation by igneous agency, 
although the conditions of these experiments were probably 
too artificial to admit of their being applied as evidence for 
the mode of production of native minerals. 
Even admitting the general proposition, that native mine- 
F rals have been produced through the agency of water, it is 
_ in very many instances difficult to furnish any satisfactory 
* The production of hydrated silicate of lime, 3 Ca O, 2 SiO; + aq. in crys« 
tals, by-melting a mixture of lime and silica with caustic potash, and of crys- 
tals presenting all the characteristic features of native chabasite, by simply 
heating fragments of palagonite to incipient redness.—See Bunsen on the Rocks 
of Iceland; Poggendorff’s Annalen, 1851, No. 6; and Scientific Memoirs, 1852. 
