Sandawana emeralds

Sandawana emeralds are small. Most of what comes out is melee, stones under a carat and often well under, and they carry a saturation of green that larger emeralds from other places struggle to reach at any size.

The geology is the classic schist-hosted emerald recipe, run at high intensity. The deposits lie along the southern limb of the Mweza greenstone belt in southern Zimbabwe, a sequence of intensely deformed Archaean ultramafic and mafic volcanics with metasediments. Pegmatites intruded into that pile. Emerald is beryl coloured by chromium or vanadium, and beryl needs beryllium, which is a granite-and-pegmatite element, while chromium is an ultramafic element. Those two things almost never occur together, which is why emerald is rare at all. Here the pegmatite carried the beryllium straight into chromium-rich rock, hydrothermal fluids did the mixing in the contact zone, and emerald grew in the biotite and phlogopite schist between them.

The stones concentrate in pockets where the pegmatite is tightly folded or the rock is sheared, which is a geologist's way of saying the good ground is where things got squeezed.

Chromium is the dominant colouring element with some vanadium behind it, and the result is a cool, faintly bluish green that a trained eye can separate from the warmer Colombian look. The locality is also unusual mineralogically: nowhere else are ilmenorutiles found carrying chromium at Sandawana levels.

This is not collectable ground. It is a controlled commercial deposit in Mberengwa District with a long and complicated production history, and access is not something a visitor arranges. Treat this pin as a place on the map that explains why the emerald in a pavé setting can be greener than the one in a solitaire.