362 
ME. N. STOEY-MASKELYNE ON THE 
The rounded character which this mineral, in common with its companion mineral the 
bronzite, presents, suggests at the first view the idea that the sudden and intense heat- 
ing which the mass must have undergone in its rapid course through the atmosphere 
may have fused, or at least softened, the surfaces of the two minerals. The rapid con- 
duction of this heat into the interior of the meteorite, to which ordinary stone aero- 
lites present much resistance by reason of the non-conducting character of their ma- 
terial, would in the case of a siderolite, where the iron forms a sponge-like and con- 
tinuous mass, be greatly facilitated by the conductive character of the metal. This 
view is encouraged by the extraordinary brittleness of the surfaces of some of the larger 
rounded specimens, which often, with the most careful handling, will fly into fragments, 
an outer crust which formed the rounded parts splitting away from a sort of inner core. 
This inner portion is found to be far less brittle, and sometimes presents an irregular 
crystalline surface with one tolerably good cleavage-plane, parallel to the plane 0 01, 
and others extremely irregular, but following approximately the directions of the planes 
of the form (1 1 0), sometimes associated with the plane 10 0, the edges of which, how- 
ever, are still often rounded. And yet it seems difficult to reconcile this explanation of 
the rounded forms and curiously merohedral character of the faces of these minerals, 
but especially of the bronzite, with the crystalline integrity of the entire grains to which 
the polarizing microscope bears evidence. 
The bronzite, indeed, will sometimes be seen in the form of little spherules like fused 
drops with no faces at all, or at times with but one or two. The silica has usually a more 
barrelled aspect, the octaid planes in particular being almost invariably, and those in the 
zone [0 01, 1 0 0] being too usually, curved from this cause. But both exhibit birefrin- 
gent characters, and the orientation of these accords with the symmetry of the crystals. 
The crystallographic elements of the silica under notice are as follow : — 
The parametral ratios are 
a : b : c = T7437 : 1-0000 : 3-3120. 
The angles, as calculated from these data and as found on seven different crystals, are 
given in the following Table, in which the different letters serve to designate the different 
crystals. The majority of these angles were measured by repeatedly observing the direc- 
OOl 
tion of maximum illumination of the planes by the telescope of the goniometer, converted 
by a lens in front of the object-glass into a microscope. 
