Estrela de Fura: an exceptional ruby of 55 ct

By Dr. M.S. Krzemnicki, first published in Facette 29 (May 2024)

Figure 1: The Estrela de Fura ruby at SSEF in February 2023. Photo: J. Xaysonghkam, SSEF.

On the 8th of June 2023, the Estrela de Fura ruby was sold at Sotheby’s in New York for a world record price of US$ 34.8 million. This ruby of 55.22 ct was cut from a 101 ct piece of rough, discovered in July 2022 near Montepuez in Mozambique, in a mine operated by the Fura Gems company.

The SSEF analysed the 55.22 ct ruby before the auction and issued one of its prestigious Provenance BooksTM, a document only reserved for rare and exceptional gems and jewellery tested at SSEF.

Microscopic observations revealed inclusions well-known from the mines near Montepuez in Mozambique, such as fine rutile needles arranged in zones, platelets, roundish amphibole inclusions, and regularly dispersed tiny whitish patches (Figure 2). Its colour can best be described as a beautifully saturated and evenly distributed red (red of medium strong saturation by SSEF standards).

Figure 2: Microphotos of inclusions found in the Estrela de Fura ruby, with fine rutile inclusions, particles and wedge-shaped platelets, tiny whitish patches, and greenish amphibole. Magnification 50x, except upper left image at 25x. Microphotos: M.S. Krzemnicki, SSEF.

Interestingly, we were able to further analyse an idiomorphic fluid inclusion (‘negative’ crystal) containing a whitish mineral phase. The Raman micro-spectroscopy analyses clearly identified this mineral as diaspore (Figure 3), an epigenetic phase formed during geological times when the ruby was slowly cooling down in the host-rock. As the analysed fluid inclusion is very tiny, the Raman spectrum of the diaspore is also showing corundum peaks from the surrounding ruby matrix. That is the reason why the corundum reference spectrum was added in the figure to visualize this overlap of peaks.

In addition to other observations (microscope and FTIR), the presence of diaspore in corundum was a further proof that this ruby had not been heat treated at any time (see also focus article in this Facette).

Figure 3: Raman spectrum of diaspore (whitish phase) detected in a fluid inclusion in the Estrela de Fura ruby. Only the diaspore peaks are labelled. Figure: M.S. Krzemnicki, SSEF.