10 KECOUDS OF THE AUSTIIAl-IAX MUiSECM. 



Avliicli ai'e approximately regular, and lience are ui' value ii) the 

 determination of the physical properties of crystals^." It is conceivable 

 tliat under certain conditions, perhaps not realisable in laboratoiy 

 experiments, the second tendency may pi-eponderate, and etching ma\' 

 result in the production of true crystal faces and these of common 

 occuri'ence ; in fact, that solution may be simply a reversal of growth and 

 produce the same faces. In a review of the publications dealing with 

 natural etch figures on beryl it is observed that several crystallographers 

 have identified certain of the figure faces as belonging to common forms. 

 Thus Peutieldi*^ enumerates the following forms on the beryl of 

 Willimantic, Connecticut, as having been developed by etching, namely, 

 (4-261), (2181), (8141), (lOU). Vrbaii determined the faces on etch 

 figures of beryl from Pisek and found such forms as (1122), (3032), 

 (2021). Kohlmanui- identified on the etch figures on the base of 

 Brazilian beiyl the forms (lOO), (3031), (3-3-6^10), (3 3 6"4), (1121), 

 Thus it is not inconceivable that etching may have led to the production 

 of common forms on the Torrington beryl also, but, if this be so, it is 

 necessary to assume that subsequent to their formation another type of 

 dissolution supervened, resulting in the gradual destruction of the faces 

 and the production of a mutilated crystal such as No. xv. (PI. ii., tig. 1). 



In the faint hope that some information of value might be obtained 

 Crystal vii. (PI. i., fig. 6) was etched in stages; the reagent used was 

 fused caustic soda. Two minutes immersion produced no visible effect, 

 but after five minutes the basal plane became pitted all over with minute, 

 apparently circular, depressions. The preexisting markings wex-e not 

 accentuated in any discernible degree, but the corrosion of the edges 

 bounding the base was . increased and the pyramid faces had almost 

 di.sappeared. After a second imniei'sion of ten minutes the etch pits 

 were distinctly hexagonal and beautifully sharp, the edges of the 

 hexagons running parallel to the edge (■//>. No figure faces could be as 

 yet distinguished on the pits. The crystal was then submitted to the 

 action of the i-eagent for fifteen minutes, resulting in an enlargement of 

 the pits, some of which now showed distinct pyramidal faces. In most 

 cases the pits terminated below in a fiat expanse of the basal plane, in 

 others they descended by steps to a point. The angles of the hexagons 

 seemed slightly rounded, but, generally speaking, the pits were quite 

 comparable, except in size, with the natural pits on crystal xii. 

 (PI. ii., figs. 4, 5). The bounding pyramidal planes of the crystal had quite 

 disappeared. On certain portions of the base were series of pits linearly 

 arranged and ovei'lapping. Hei-e and there were obsei-ved residuals in 

 the form of narrow, Hat-topped ridges. These, on being inspected by 

 hand lens and microscope, wei-e seen to have an irregular wavy, almost 

 conclioidal surface. The crystal was now mounted on flie goniniiu'ter 



" McNaira — A/«r. ,'il., p. 2'iH. 



'" IVntii'M A ■. .Inuiii. Sci.. xl.. IH'.Kf. p. t'to. 



" Vrliii.- ZrilH. Fvry.sl., x.xiv., \H\,Ki. \>\k 101-112. 



I- Koliliimim--Ni'uos Jiihrb. Miu., I!eil.-lkl. xxv., 1907, i'. 17*. 



