The Largest Faceted Cerussite Gem in the World

The Light of the Desert is a cerussite gem in the Royal Ontario Museum's collection. It is the world's largest faceted cerussite gem, weighing 898 carats (179.6 grams). Cerussite is a lead carbonate mineral that is extremely fragile and sensitive to temperature changes and vibration. The Light of the Desert was discovered in Tsumeb, Namibia, in the 1960s and was cut and polished in Arizona. It was acquired by the Royal Ontario Museum in 1984.

The cutting and transport of this gem is a delicate business as cerussite is extremely fragile and sensitive to changes in temperature changes and vibration. After it was cut in Arizona, the gem was placed in a box, then wrapped in a large woolen scarf and a winter vest, and then hand transported to Toronto for display.

Cerussite is a popular collection mineral. It is famous for its great sparkle, great density and amazing twinned crystals. Cerussite is a minor ore of lead. It has a very high luster due mostly to the lead content. Just as leaded crystal glass sparkles more brilliantly because of its lead content, so too does cerussite.

The Largest Faceted Cerussite Gem in the World. Museum Cut Cerussite gem, 896 cararts, from Tsumeb, Namibia

The lead raises the index of refraction of cerussite to just over 2.07. The lead is also responsible for its increased specific gravity. Cerussite has one of the highest densities for a transparent mineral. It is over six and a half times as dense as water. Most rocks and minerals average only around three times the density of water.

This mineral can form some geometrically intricate structures and spoked star shapes that simply are amazing. Cerussite belongs to the Aragonite Group of minerals. A group that as a whole is well known for twinning with commonly twinned members such as aragonite, witherite and strontianite Twinning is most definitely common in cerussite and besides the intricate structures mentioned already, singular twins are also interesting.

There are three basic types of twinning in cerussite: Elbow or chevron shaped twins, cyclic twins and last but not least, reticulated twins. The elbow or chevron shaped twins are the most common and are generally seen on most specimens. The cyclic twins often form star shapes with six "spokes" extending from the star. Very beautiful! The reticulated twins are classics and form complex interconnected beams of crystals. So intricate are these specimens they appear to have been constructed. They truly are an awesome mineralogical wonder. Cerussite twins are a must for collectors who are fond of twinned crystals.

Cerussite is known for its dispersion (or fire). Dispersion is the amount of light a gem will pass through the colour spectrum.

Cerussite is one of the only gems with adamantine (diamond-like) luster.