Largest cut tsavorite garnet

The largest cut tsavorite garnet is 325.13 carats with dimensions of 42.11 x 36.46 x 28.34 mm as assessed by Dr Adolf Peretti at the GRS Gemresearch Swisslab in Bangkok, China, on 6 November 2006. The rough stone, which weighed 185 g (6.5 oz), was found in the Karo Block B mine in the Merelani Hills of Tanzania, as documented by Dr Henry Hänni of the SSEF Swiss Gemmological Institute.

First discovered by British geologist Campbell R Bridges in 1967, tsavorite is named after the Tsavo Game Reserve (now Tsavo National Park) in southern Kenya, near the border with Tanzania, where it was initially found. It has subsequently also been mined in northern Tanzania (at sites traditionally used to source tanzanite), with smaller deposits uncovered farther afield in Madagascar, Pakistan and Antarctica.

The calcium-aluminium garnet, with the chemical formula Ca₃Al₂Si₃O₁₂, is highly prized for its hardness, rarity (some 200 times rarer than emerald), high refractivity and most importantly vibrant green colouration, caused by traces of vanadium of chromium.

Clear tsavorites greater than 10 carats are rare so this is an exceptional specimen. Prior to this the largest-known cut tsavorite, also originating from the Karo mine from earlier in 2006, was 120.68 carats with dimensions of 34.70 x 25.30 x 17.50 mm. Another large example, dubbed the “Lion of Merelani”, weighs 116.76 carats (refined from a 283-carat rough stone); it was in part gifted in 2023 to the National Gem Collection, housed at the Smithsonian National Museum of Natural History in Washington, DC, USA, by Bruce Bridges, the son of the geologist that first identified the gem in 1967.

It’s worth noting that some geologists in Kenya have questioned whether the green garnets found in Tanzania are truly tsavorites owing to their lighter colouration; whereas the ones mined in Kenya tend to be a darker shade of green.