REPORT ON MINERALOGY. 
347 
tion of this problem. Thus in a Memoir which appears in the 
Transactions of the Wernerian Society of Dresden for 1818, 
Breithaupt conjectures that boron is the ingredient which gives 
the electrical and crystalline polarity which he attributes to 
boracite, tourmaline, anatase, and axinite. Hitherto, however, 
conjectures and researches on this subject have had little 
success. In the course of last year, Magnus endeavoured to 
detect the chemical difference of garnet, a tessular, and idocrase 
a pyramidal substance ; yet after many analyses and conjectures 
he was obliged to acknowledge that it had escaped him. Berzelius 
{Brewster s Journal, N.S. iii. 188.) finds no difference between 
the composition of hexahedral and prismatic iron pyrites. More 
recently still, Ampech has analysed a number of tessular mi¬ 
nerals, spinelle, pleonaste, gahnite, franklinite, and chromic iron 
oxide : and in this instance he seems to have had some success in 
giving a common type to their chemical formulae, as there is a 
common type in their crystallization. According to him, they 
consist of ingredients of two classes: the one class containing alu¬ 
mina, protoxide of chrome, peroxide of iron or manganese ; the 
other class containing protoxide of zinc or iron or magnesia; and 
the rule of composition is, that the ingredient of the former class 
contains three times as much oxygen as that of the latter. If 
this law be true, we cannot doubt that many similar laws exist 
both for tessular and for other forms, and we may hope that 
after one has been detected others will soon appear. 
The discovery of artificial crystals in the slags of furnaces 
was not unimportant to the chemistry of mineralogy. One of 
the first and most extraordinary instances was the detection of 
perfect crystals of titanium in the Welsh iron slag, by Dr. Wol¬ 
laston and Professor Buckland. It has appeared by examina¬ 
tion that these accidental products are more free from any ad¬ 
mixture of iron than it is easy to obtain titanium by the ordinary 
chemical processes. In 1825 Mitscherlich found in the Swedish 
furnaces bisilicate of iron (pyroxene), mica, and other mineral 
species. About the same time, Berthier in France obtained 
in the furnace, by direct synthesis, regulated by the atomic 
theory, crystals similar to those found in nature. Professor 
Miller of Cambridge has examined several slags from the fur¬ 
naces in Wales, and it appears that the crystals in those assume 
the form of olivine. It is satisfactory thus to find that the same 
substances affect the same crystalline form in our furnaces and 
laboratories, and in the great laboratory of nature. Indeed 
nothing can be more likely to help us in obtaining a knowledge 
of the chemical laws of crystalline forms, than to have the power 
of verifying our conclusions synthetically by forming crystals, 
as well as analytically by destroying them. 
