40 ze MINERALOGY AND LITHOLOGY. 
is always opaque. It very rarely appears crystallized, but is generally 
in bits and patches of very irregular and indeterminate outline. It is 
often seen in staff-like, club-shaped, and other elongated forms, and often 
in indented and diffuse forms, which, although not sufficient to distin- 
guish it from magnetic iron, are certainly quite characteristic of titanic 
iron. When crystallized, it is hexagonal; and in some of our rocks 
hexagonal and rhomboidal plates are found which are suspected to be 
of titanic iron. 
Although menaccanite is difficult to dissolve in acids, yet it undergoes 
a peculiar kind of decomposition in the rocks, which is quite character- 
istic of it. This decomposition is very often seen in microscopic study 
of basic rocks. Its beginning is shown in grains that have a gray, trans- 
lucent edge. Then, again, this gray substance traverses the black grain 
in straight lines, following the cleavage or planes of composition; then, 
but a faint skeleton of black mineral is seen traversing the white decom- 
position product; and, finally, every trace of the titanic iron has disap- 
peared, leaving a gray, translucent mass, which by reflected light is 
white, and which possesses a structure dependent on the mode of its de- 
composition. The white product resulting has been determined by Prof. 
A. von Lasaulx to be a compound of titanic acid and lime resembling 
perofskite [Ca Ti Os]. It is supposed that the lime of the hornblende 
or feldspars reacts on the titanic iron, producing the titanate of lime; 
and sometimes, when silica also takes part in the decomposition, sphene 
may be produced. Where the iron goes to is not explained, but it 
is likely that it enters into the composition of the ferruginous chlorites, 
which are so usual in these basic rocks where this mineral is most 
common. 
The forms that the decomposition product takes, are most remark- 
able; and in our New Hampshire diorites are some more strange 
than have been seen elsewhere. When the decomposition goes on 
regularly from the circumference till it reaches the centre, the re- 
sult is a mere irregular patch of translucent material, but when it fol- 
lows the cleavage or lamination the forms are quite fantastic; and at 
times these forms possess such a very strange similarity to organisms, 
that they have deceived observers into the belief that they were the fos- 
silized remnants of microscopic forms of life that existed in the original 
