The Royal Ontario Museum houses the world’s largest faceted specimen of a mineral called Cerussite. Cerussite, from the Latin “white lead”, is a lead carbonate mineral with the chemical formula PbCO3.
Cerussite is especially interesting to jewelers and gem enthusiasts because of its extreme dispersion or fire. Dispersion is a gem’s ability to split light into prismatic colours. The desirable sparkle and flash a diamond displays is nothing compared to the vibrant dispersion of Cerussite.
Diamond lovers can rest easy knowing that fragile Cerussite will never become the gem of choice despite its colour and flash. Besides only having a mohs hardness between 3 and 3.5 (quite soft!), Cerussite is very sensitive to heat and vibration. The specimen of Cerussite on display at the ROM is called the “Light of the Desert”, and weighs an astounding 898 carats and is approximately four times the size of the next largest faceted specimen. Considering how fragile Cerussite is, the “Light of the Desert” is an amazing feat of gemstone faceting.