364 
ME. N. STOEY-MASKELYNE ON THE 
reflecting plane 1 1 0 on the crystal C. In fact the faces of the form (1 1 0), though 
parallel to what appears to be a somewhat difficult cleavage, never present a good even 
reflecting surface, being generally more or less conchoidal when cleavage-surfaces, and 
dull when natural faces. 
The cleavage-plane 0 01 has a vitreous lustre ; the lustre on the planes of the forms 
10 0 and 1 0 1, as also of the rounded surface in the zone with them, is usually of a 
resinous character, strongly recalling that of opal. 
It has already been observed that the faces of the octaid forms are almost invariably 
rounded. Fair approximate measurements, however, of three of the faces in the zone 
[0 01, 110] on the crystal C were obtained; and one octaid plane on that crystal, 
repeated in two octants, gave measurements that accord fairly with the somewhat 
complex symbol 5 4 8. This face, though not giving a reflected image, is the best octaid 
plane upon the crystal. 
That the mineral belongs to the rhombic and not to a uniaxal system is emphatically 
evidenced, independently of these measurements, by its optical characters, as shown in its 
very distinct and widely separated optic axes. As has been said, the first mean line is 
the normal of the face 10 0, that to face 0 0 1 is the second mean line. The first mean 
line is parallel to the axis of least optical elasticity, so that the crystal is positive in 
its optical character. The apparent angle, as measured in air, of the optic axes was 
approximately determined as 107° to 107° 30'. The axes for the red rays are slightly 
more dispersed than those for the blue. 
The crystalline grains which constitute this ingredient of the meteorite, when first 
obtained, are of a rusty brown and sometimes even black colour ; treatment for a short 
time with dilute hydrogen chloride, however, entirely removes this iron stain and leaves 
the granules in a state of colourless purity, in which state they are readily distinguished 
from the grains of the accompanying bronzite. 
The specific gravity of the mineral gave the number 2 ‘245. Its hardness is 5'5. 
Two analyses were made by different methods, and the results are given below. 
I. 0-3114 substance, distilled with pure hydrogen fluoride, gave 1-1136 gramme of 
potassium fluosilicate, 0-0035 gramme iron oxide, 0-0018 calcium oxide, and 0-0132 
gramme magnesium phosphate. 
These determinations denote the following percentages : — 
Silicic acid 9 7 -4 3 
Iron oxide 1-124 
Calcium oxide .... 0-578 
Magnesium oxide . . . 1-509 
100-641 
II. 0-2653 gramme of carefully selected substance, evaporated with an excess of 
ammonium fluoride, left 0-0021 gramme residue, chiefly iron oxide. 
This determination denotes the following percentage composition : — 
