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.