58 Prof. G. H. F. Ulrich. On a Meteoric Stone 



rotation of the stage, the extinction is undulating, approximately 

 parallel to the fibre-lines, but a multitude of minute granules and 

 lath-shaped bodies always shine out brightly along the darkened 

 fibres. As in the case of the olivine, none of the sections show altera- 

 tion of the mineral to serpentine. 



Glass and a substance resembling Glass. — These require to be 

 described together, because of their mode of occurrence and their like- 

 ness in common transmitted light. They are both perfectly colour- 

 less, transparent, and occur pretty abundantly, though mostly in small 

 particles, filling generally larger and smaller crevices between the 

 grains of olivine or of olivine and enstatite; their limpidness, com- 

 bined with absence of colour, rendering them easily distinguishable 

 from these minerals. The difference between the two substances 

 consists in the one — the glass — being perfectly isotropic, the other 

 anisotropic. The large finely-dotted patch near the centre of fig. 5, 

 and the similarly dotted belt, enclosing several clear spaces, which 

 extends in fig. 6 from the lower edge through the centre towards the, 

 upper edge, consist largely of the real glass. They show between 

 crossed nicols a dark background, as it were, speckled with in- 

 numerable bright granules, polarising in fine colours, therefore, no 

 doubt, olivine ; and though on rotation of the stage the dark ground 

 brightens up granular-like in many places, still there are numerous 

 spots which remain perfectly dark throughout a complete rotation. 

 In fig. 4 a large rather ill-defined olivine chondrule is delineated, 

 in which the clear (undotted) parts on the right and left of, and also 

 within the main part of the olivine near the upper edge, consist all 

 of the anisotropic glass-like substance. For whilst between crossed 

 nicols each separate particle shows dark and light spots — the light 

 ones extinguish and the dark ones brighten up on rotating the stage — 

 the extinctions are not, however, sharply defined, as in the former 

 case, but cloudy or undulating, and there is also no chromatic polar- 

 isation. All things considered, it is very probable that the anisotropic 

 substance simply represents glass in various stages of devitrification. 



Nickel-Iron. — This is indicated in the figures by the dotted and 

 cross-shaded areas, and is easily recognisable in the sections in re- 

 flected light by its metallic silvery-white lustre. As seen by com- 

 parison of the figures, it occurs in relatively large proportion, but is 

 rather unequally distributed through the stone. The particles are 

 highly magnetic and vary from very minute specks to such as 

 approach a grain in weight. One such, for instance, was found on 

 grinding a sample of the stone for chemical analysis. Larger particles 

 sometimes enclose small grains of olivine, as shown in fig. 2 near the 

 left-hand edge, and there occur also portions in some of the sections 

 in which the iron forms a kind of rude network the meshes of which 

 are occupied by olivine. 



