. Annals of the New York Academy of Sciences. Science; Science -- New York (State). FENNER, THE WATCHING BASALT 127 large areas, and the onl}'- trace of it left is a hazy or muddy appearance of the prehnite. In many places, the patches of turbid material within the prehnite still show in their outlines the appearance of albite groups. In slide 65, a similar process of replacement has produced the results shown in fig. 6. As in slide 62, veinlets of albite and prehnite are found cutting a crystalline basalt. The albite lies next to the walls and gives way rather abruptly to prehnite, but a few
. Annals of the New York Academy of Sciences. Science; Science -- New York (State). FENNER, THE WATCHING BASALT 127 large areas, and the onl}'- trace of it left is a hazy or muddy appearance of the prehnite. In many places, the patches of turbid material within the prehnite still show in their outlines the appearance of albite groups. In slide 65, a similar process of replacement has produced the results shown in fig. 6. As in slide 62, veinlets of albite and prehnite are found cutting a crystalline basalt. The albite lies next to the walls and gives way rather abruptly to prehnite, but a few outlying crv'stals of albite, greatly corroded, appear to have survived within the prehnite at some distance from the walls. Still farther out, phantom forms of former albite crystals are outlined by a slight turbidity in the prehnite. They are completely replaced by prehnite and can be connected with albite only by the appearance of the terminal crs'stal faces. These, however, are characteristic. The radiating and fanlike groups of prehnite crystals J^re/inite A/ate Phan toms. Aa;tc Fig. G. Replacement of albite by preliuite. Phantom forms of former albite crystals are dimly perceptible. X 35. Slide 65. are superimposed upon the former structure of the albite, but in places the albite has had an influence upon the crystallization of the prehnite. In slide 63, minute veins similar to those described are filled with albite and datolite. The albite crystals occur in interlocking aggregates of varying crystallographic orientation. In places, they occupy the veins to the exclusion of all other material, or they may project at various angles from the sides of the vein into masses of datolite. Crystals up to mm. in length are not uncommon, and the general average of size is noticeably larger than the plagioclase rods in the walls. In most places, there is no evidence of corrosion of albite at contact with datolite, but in some areas, phenomena of replacement similar to those whic
Size: 1618px × 1545px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjectscience, bookyear1879
