A new type of mineral species named Laurentthomasite and bearing an intense deep blue hue has recently emerged in the coloured gemstone sector.

Named after French mineral dealer Laurent Thomas, the stone was discovered in Madagascar’s Toliara Province and was approved by the International Mineralogical Association as a new species of mineral group milarite in April 2019. 

Earlier this year, two facetted greenish-blue stones that were supposedly Laurentthomasites were sent to the Gem and Jewelry Institute of Thailand (Public Organization) – Gem Testing Laboratory (GIT-GTL) for identification.

According to the lab, the stones were tested using both standard and advanced gemmological instruments. Standard verification revealed that the stones have a refractive index of 1.555 to 1.560 and a birefringence of 0.005. They are doubly refractive, uniaxial positive and inert to long- and short-wave UV radiation.

The stones’ most prominent characteristic however is their strong dichroism in greenish-blue and light greenish-yellow. Microscopic observation meanwhile showed various inclusions in the stones such as “fingerprints,” negative crystals, and two-phase formations, noted GIT-GTL. 

“The chemical data obtained are consistent with the formula of Laurentthomasite. The Raman spectrum indicates a close association with milarite,” the lab revealed. 

While the stones’ gemmological characteristics are similar to milarite, Laurentthomasite has a distinctly different colour than milarite, which is colourless to pale yellow or green, explained GIT-GTL.