R. H. Rastall — Minerals of Lower Greensand. 267 



ilmenite. The most noteworthy and unusual feature is the presence 

 of numerous crystals of sphene. 



Sphene is quite abundant in crystals -which are as a rule much 

 rounded and chipped, but still show the characteristic lozenge 

 shape. They are easily distinguished by their pale-yellow colour, 

 very high iudex of refraction, which gives a broad black border, and 

 very strong birefringence : crystals of the usual size generally give 

 colours of the fourth order. Owing to the high refractive indices 

 and strong dispersion the crystals when in the position of extinction 

 between crossed nicols often show curious prismatic colours, which 

 afford a useful indication of the mineral. Inclusions are very 

 abundant, both circular bubbles of gas (or glass) and minute needle- 

 like crystals. Fig. 6 shows a sketch of an unusually well-formed 

 crystal of sphene, with both kinds of inclusions. 



FlG. 5. — Quartz grains, Parish Sand Pit, 

 Aspley Guise, x 50. 



Rutile is also common in the usual red grains, generally much 

 rounded and corroded. In a few crystals the colour is quite unusually 

 deep. There are also orange or yellow crystals still sufficiently 

 undamaged to show crystal-faces. Kyanite is abundant in large 

 angular flakes and blades of quite normal character. Staurolite is 

 very common in good-sized angular fragments of an orange-yellow 

 colour. These need no special description. Tourmaline is fairly 

 abundant, both the common brown variety in drop-like grains and 

 in good crystals, together with a few more angular grains of an 

 extraordinarily deep blue colour. Muscovite is very common in 

 small flakes and a few broken crystals of pyroxene were also seen. 

 The opaque iron ore is ilmenite. One very fine tabular plate with an 

 etched surface shows the rhombohedral symmetry of the etched 

 figures on the crystal faces. 



Other samples taken from different parts of the same pit differ 

 from the one described above chiefly in the much lower proportion 



