MINERAL CONSTITUENTS OF METEORITES. 
205 
are mechanically separated and examined, it is not difficult to distinguish what seem to 
be three different minerals. One is rare ; it is colourless and transparent, and may be 
obtained in small splinters that have the appearance of being the result of a definite 
cleavage. The little planes thus obtained are too often merely divisional surfaces without 
crystallographic significance ; and where they possess a more definite character, they 
present such rude faces that the values obtained for the angles can rarely be relied on. 
Another form of the mineral mass is that of a grey semitransparent splintery mineral, the 
fragments being generally very composite. From these two varieties I failed in obtaining 
the measurements of an entire zone, the planes in which belonged to the same indi- 
vidual, and the attempt to cleave these minute individuals apart only serves to destroy 
them. The third form is that of a dark grey glistening crystalline substance tabular in 
form and very opaque. It presented cleavages indistinctly marking the faces of a prism, 
f88° 35' j 
for which the mean of several measurements gave an angle of j' Q / !• ; and to the 
planes (1 1 0) of this prism a dull face (0 0 1) is perpendicular, which seems in this case 
to be a second and less facile cleavage. 
The results subjoined were obtained from seven selected fragments of the other forms 
of this mineral. They lack the important check which the polariscope affords; for the 
substance was usually too opaque for the use of this instrument, or else too composite 
to give any value to the results obtained with it. The fragments experimented upon 
were extremely minute and fragile, often breaking into powder while being mounted for 
the goniometer, and the angles are necessarily only approximate. 
Found. 
In Breitenbach enstatite. 
10 0 110 about 46 
1 1 0 1 10 87 10 to 88 
100 101 41 34 
010 0 1 1 * about 40 
45 52 
88 15 
41 12 
40 21 
The planes 10 0 and 110 are cleavages. In some cases, generally where the crystals 
are very composite, a cleavage seems to run parallel to a plane inclined at 73° to 74° to 
the face (1 0 0) and 90° to the face (0 1 0). As the forms of the mineral presenting this 
plane contain calcium, I have been uncertain whether to attribute the importance of 
this plane in certain specimens to an intermixture of augite with the enstatite. The 
plane 1 0 4 is also a conspicuous one on the crystals of enstatite in the Breitenbach 
meteorite, and the angle (74° 4') which it makes with the plane 1 0 0 in that mineral is 
very near that of the inclination (73° 59') of the planes 10 0 and 0 0 1 of diopside. 
The chemical analysis of these three minerals shows that they are really enstatite 
under different aspects. Where the substance contains no lime it presents itself as a 
simply prismatic mineral, the dark grey tabular variety ; where lime is present, though 
to the amount of less than 2 per cent., the crystalline structure becomes more complex, 
* A dubious plane. 
2 E 
MDCCCLXX. 
