Himalayan garnets

Sample GF403 - ??location??\

Himalayan garnets from the Langtang valley show spectacular zonation in Ca- contents, testifying to a complex, multistage growth history. Sample GF403 preserves an internal euhedral Ca-rich core with a broad low Ca-rim, as can be observed in the shaded image below.

The compositional profile along the line a-b-c shows two discrete compositional "plateaus" in the garnet (either side of point b). The different zones are separated by narrow transition zones with the classic "error function" profiles associated with diffusional processes.

The euhedral nature of the core is illustrated in the 3-D perspective below.

 

Sample GF373 - ??location??

More complicated zonation patterns are found in sample GF373. In this sample the Ca content shows a gradual reduction from core torim, with some narrow oscillatory zonation near the margin of the crystal (top right corner).