1870.] 



Mineral Constituents of Meteorites. 



151 



presence of this metal of the zirconium group in the augite itself, — an 

 assumption confirmed by experiment. The dichroism of this augite is 

 strongly marked, especially through the face 0 10, which in one position 

 exhibits a tint resembling that of the blue anatase of Brazil, due apparently 

 to minute scales permeating the crystal, and visible only in the microscope. 

 These scales may possibly be the Osbornite sufficiently thin to be trans- 

 parent, and may be the cause of the beautiful golden metallic reflection 

 which characterizes the face 1 0 0 of the augite. 



VI. The Augitic Constituent of the Busti Aerolite. 



Associated with the spherules of Oldhamite that have been described as 

 occurring in a nodule of this aerolite, and less plentifully distributed 

 through the rest of its mass, is the silicate already alluded to as a variety 

 of augite, and as containing traces of titanium or zirconium oxide. This 

 silicate occurs in crystalline grains of a pale violet-grey colour, intimately 

 mixed with another silicate presently to be described. "When isolated, 

 these grains present a few crystal faces, among which one as a cleavage- 

 plane is prominent. So imperfect are the rest, that they furnished reli- 

 able measurements only with extreme difficulty. These determinations, 

 however, together with its optical characters, proved that the mineral 

 belongs to the oblique system. The measurements gave the following 



approximate values : — 













Angles found. 





Angles of diopside. 



001 



100 



About 75° 30' 





73° 59' 



00 1 



1 10 



About 81° 





79° 29' 



1 1 0 



100 



45° 54' to 47° 



26' 



46° 27' 



1 1 0 



1 1 0 



85° 8' to 86° 



20' 



87° 5' 



1 00 



1 1 1 (?) 



53° 25' to 54° 



15' 



53° 50' 



001 



1 1 0 



100° 8' 





100° 57' 



The plane containing the optic axis is perpendicular to the edge 10 0, 

 10 0, and the optical character in the centre of the field is negative on 

 looking down the second mean line, which makes angles about 22° 45' 

 and 52° 30' with the normals to the faces 0 0 1 and 10 0 respectively. 



Two analyses of this mineral by the method described gave the follow- 



ing results : — 



L H. Mean oxygen ratios. 



Silicic acid 55*389 55*594 29*928 



Magnesia 23*021 23 036 9*331 



Lime 20*02 19*942 5*709 



Iron oxide 0*78 0*309 



Soda 0*554 [0*554] 



Lit hia trace [trace] 



100*364 99*435 



