4 RF.COnDS OF TUF ArSTRAI.lAN MPSFFM. 



I'rvstal i. (PI. i., fiprs. 1, 2) mensnres ?> X !■•'> ('"i- ^» colonr it is 

 ail aqnamaiine of good qnality but iiiucli flawed internally. The 

 pi-isms are strongly striated vertically but the base is perfectly 

 smooth and devoid of markings. The principal faces ai*e c (0001), 

 (f (1120), ))i (1010), // (1011), and u (2021); two small faces of v (2131) 

 are present. Between the prisms and pyramids there is a narrow etched 

 band shown in the tignre as a stippled area ; i-eflections weie obtained 

 from thi.s band, the angle p varying from (58^ 15' to (t9" 2(>' with a mean 

 of t)8' 55'. This indicates a form (90l»2), hitherto undescribed, for which 

 the calculated value of p is 68° 5(5'. As this is clearly a prerosion face, I 

 have not assigned a letter to it. 



Crystal ii. is essentially similai' to No. i. but it is much smaller, 

 measuring 1*4 X '^ cni » ^^^^ almost colourless. It shows nearly the same 

 combination with the absence, however, of k and v ; /( is relatively nari-ow. 

 There is the same etched zone between the piisms and pyramids and the 

 average i-eading for the i-eflection obtained gave an angle p of QS° 47' 

 wliich agrees well enough with that obtained in crystal i. and the 

 calculated angle for (9092). 



Crystal iii. resembles Nos. i. and ii. but here tlie prerosion form seems 

 to be $ (80.S1) for the avei-age value for p is 59'' 5:V (calculated 59^ 59'). 



Crystal iv. measures 11 X "5 cm. It has the usual etched zone 

 between pyi-amids and pi-isms and the pyramids themselves are slightly 

 attacked. 



In Ciystal v., which measures 1-4 X '7 cm., the etching has almost 

 obliterated the small faces of p, n, and s, replacing them by a rough 

 surface from which no distinct reflections could be obtained. The base is 

 slightly attacked and shows a number of lines and roughly hexagonal 

 jnarkings, mainly depressions, the lines and boundaries i tinning parallel 

 to the edge r/ji. The prism faces show markings which are oblong or 

 irregular elevations and depressions, the long directions of which are 

 parallel to the vertical axis. 



Crystal vi. (PI. i., tig. 4) from Heffernan's mine, measures 3 < 1"9 

 cm.; only the termination is shown in the Hgnre. The etching is here in 

 »he early stages ajid consists of a band between the prisms and pyramids 

 which is pitte<l and i-ough but exhibits no detinite figures and yields no 

 satisfactory reflections. The base is large and diversifled by a nnmbei' of 

 lines and hexagonal maikings as indicated in the Hgui-e, the dii-ections of 

 the lines and tlie boundai'ies of the mai-kings being that of the edge 

 between <■ and /». Under the microscope the markings reveal themselves 

 as slightly laised poi-tions of the base bounded by nan-ow planes of ^>. 

 The ci-ystal is composed of two or possibly three portions not quite in 

 jtarallel position and shows a numbei- of gi-owth zones consisting of 

 successive hexagonal shells, the outer shells being paitly stripped ott'. 

 Three snnill planes of )i (;{l4l) were identilietl on this ci-ystal, this being 

 the only instance of their occurrence on the Torrington beryl. 



