Abstract
An unusually well-developed perthitic intergrowth of microcline and albite was discovered in pegmatite masses occurring in syenite near Tory Hill, Haliburton County, Ontario. The intergrowth is a composite of several textural varieties. The predominant type is composed of albite spindles developed parallel to the prism directions (110) and (110) in the microcline. The spindles or blebs along each of these crystallographic directions are arranged en echelon and the two sets are superimposed in such a manner as to result in braid-like veins which are approximately parallel to (100). Striking features of this perthite are the uniformity in orientation and size of the blebs, and the high percentage of the albite. The name, braid perthite, is introduced as a descriptive term for this textural type.
En echelon grouping of albite films (film perthite), as well as of the albite spindles of the braid perthite, is characteristic of the Tory Hill feldspar. This textural feature is also recognized in other perthites, and en echelon arrangements may be characteristic of early-formed blebs which by later processes are converted into solid veins or bands. In the Tory Hill perthite, vein or band perthite and patch perthite have been developed from the braid type by replacement. The feldspar components calculated from the chemical analysis of the Tory Hill feldspar are (weight percentages) Ca-f, 0.1; Na-f, 57.7; K-f, 42.2.
The crystallographic directions developed in the Tory Hill perthite are similar to those found in other perthites. It is believed that these directions are related to, and basically controlled by, the atomic structures of the interlaminated feldspars. Similarities between the Tory Hill feldspar and Ceylon moonstone are noted, and the origin of these perthitic feldspars may have points in common. Exsolution and replacement probably accompanied by recrystallization are the processes favored to explain the origin of the feldspar.
