Ugrandite Garnet

Ugrandite is a series name for the calcium garnets, built from its three members: Uvarovite, GRossular, and ANDITe (andradite). All three contain calcium in the same structural site, while chromium, aluminum, and iron substitute in another.

This series contains some of the most valuable garnets: emerald-green uvarovite (chromium), the many-colored grossular (including tsavorite and hessonite), and andradite (including the brilliant green demantoid). Ugrandite is the counterpart to the aluminum garnet series, pyralspite.

The framework helps describe the real chemistry of calcium-rich garnets, which are usually intermediate compositions like grandite.

Ugrandite garnets form chiefly in calcium-rich metamorphic and metasomatic settings. Grossular and andradite are classic skarn minerals, crystallizing where intrusions react with limestones and dolomites. Uvarovite forms in chromium-bearing serpentinites and chromite deposits.

Because aluminum and iron substitute freely, grossular and andradite blend into intermediate grandite. Notable localities include the chromite belts of Russia and Finland (uvarovite), East African gem gravels (tsavorite grossular), and skarns worldwide (andradite, demantoid).

Ugrandite garnets are isometric, with vitreous to adamantine luster, white streak, conchoidal fracture, and no cleavage.

• Hardness: 6.5-7.5 (slightly softer than pyralspite).
• Optic character: singly refractive (often with weak anomalous birefringence).
• Color: green (uvarovite, tsavorite, demantoid), honey/orange/cinnamon (grossular, hessonite), yellow to black (andradite).

High dispersion (fire) flags andradite/demantoid. Calcium garnets more often show anomalous birefringence than pyralspite, a useful diagnostic.

Ugrandite supplies several premier gem garnets: tsavorite, demantoid, hessonite, and the rare uvarovite. These are faceted for high-value jewelry, with demantoid prized for its fire and tsavorite for its vivid green.

Uvarovite is also popular as a sparkling green druzy mineral specimen. Calcium garnets have minor industrial uses. Metaphysical associations follow those of garnet generally and are not scientific.