gemmology.dev – Zimbabwe — Sandawana Emerald and Marange Diamond

Introduction

Zimbabwe hosts two internationally significant gem deposits. The Sandawana Mine
in the Belingwe (Mberengwa) district, Midlands Province, has produced emerald since
the early 1950s from ultramafic rocks (talc-chlorite-carbonate schists) of the
Belingwe greenstone belt in contact with granitic intrusions. Sandawana is celebrated
for intensely saturated, pure grass-green emerald (Cr³⁺ dominant with very low Fe,
yielding some of the strongest red LWUV fluorescence of any natural emerald) but
almost invariably in very small sizes: commercial material is typically 0.1–0.3 ct,
stones above 1 ct are exceptional. Tremolite needles (calcium magnesium amphibole)
are the primary diagnostic inclusion, confirmed by Raman microspectroscopy by Zwaan
and Burke (1998).

The Marange alluvial diamond field (Manicaland Province, found 2006) is commercially
large but gemmologically less characterised; it became controversial due to human
rights concerns and Kimberley Process scrutiny, and many stones require treatment
(HPHT or fracture-filling) to improve appearance. ^[1]^[2]

Sandawana Emerald — Overview

The defining characteristics of Sandawana:

Discovery and History

Sandawana Mine (Belingwe/Mberengwa district, Midlands Province); mining
established by the early 1950s; the name derives from the local Karanga word
Gained international attention from the 1960s for intensely saturated crystals
Zwaan, Kanis, and Petsch (1997): "an intensely saturated, pure green colour
comparable to Colombian emerald, but they are generally small" ^[1]

Geological Setting

Hosted in ultramafic rocks (talc-chlorite-carbonate schists derived from
serpentinite) of the Belingwe greenstone belt; at the contact with granitic
intrusions
Emerald in talc-carbonate veins and chlorite-schist envelopes around
quartz veins; Cr from the ultramafic host; Be from the granite
Oxygen isotope study (2004): Confirmed a fluid-mixing genesis at the
schist-granite contact; meteoric + magmatic/metamorphic fluid mixing

Sandawana Colour and Fluorescence

Optical characteristics:

Colour: Vivid, pure grass-green to emerald-green; colour saturation among
the highest of any natural emerald; often described as "vivid green" without
blue modifiers (the emerald equivalent of "pigeon blood" quality)
Chromophores: Cr³⁺ dominant; minimal V; very low Fe; the low Fe is the
key to the exceptional colour purity and very strong red fluorescence
UV Fluorescence (LWUV): Very strong red; one of the highest Cr-driven
fluorescence intensities among natural emeralds; significantly stronger than
Zambian (higher Fe) or Colombian material
Chelsea Colour Filter: Strong red (Cr dominant)
Size constraint: Almost invariably <0.5 ct commercial material; 0.1–0.3 ct
typical; stones >1 ct are exceptional and command premium prices

Diagnostic Inclusions — Tremolite Needles

Additional Sandawana Inclusions

Complete inclusion suite:

Talc (soft, platy), from the talc-schist host
Chlorite flakes
Dolomite and calcite rhombs
Two-phase fluid inclusions (liquid + gas)
Apatite (rounded crystals)

Sandawana Origin Determination

Combination criteria virtually diagnostic for Sandawana:

Very high Cr with very low Fe: High Cr/Fe ratio contrasts with Zambian
and Brazilian material; LA-ICP-MS is confirmatory ^[3]
Tremolite needle inclusions: Primary visual diagnostic ^[2]
Very small crystal size: <0.5 ct in virtually all commercial material
Strong red LWUV fluorescence: Very strong; much stronger than most other
emerald origins at equivalent saturation

Sandawana vs Key Emerald Origins

Feature	Sandawana (Zimbabwe)	Colombian (Muzo)	Zambian	Ural (Russia)
Diagnostic inclusion	Tremolite needles	Parisite + halite in 3-phase	Biotite mica	Phlogopite mica
Fe content	Very low	Very low	Moderate–high	Low
Cr content	Very high	High	Moderate	Moderate
LWUV fluorescence	Very strong red	Strong red	Moderate red	Moderate red
Typical size	Very small (<0.5 ct)	Wide range	Small to medium	Small to medium
Li content	>200 ppmw	<200 ppmw	>200 ppmw	>200 ppmw

Marange Diamond (Zimbabwe)

The Marange alluvial diamond field:

Discovery and Controversy

Marange (Manicaland Province, eastern Zimbabwe): One of the largest alluvial
diamond deposits discovered in the 20th century, found in 2006 ^[4]
Stones distributed through fluvial and aeolian gravels overlying kimberlite
Became controversial due to alleged human rights abuses; Kimberley Process
imposed scrutiny; exports were blocked then reinstated

Gemmological Profile

Marange diamonds span from heavily included, graphite-laden brownish-grey
stones (most common) to rare near-colourless and fancy yellow material
Many stones commercially treated (HPHT or fracture-filling) to improve appearance
Standard gemmological identification methods apply; no diagnostic inclusion
suite unique to Marange has been documented in peer-reviewed gemmological
literature retrieved from the research database

Zimbabwe — Sandawana Emerald and Marange Diamond