The Logan Sapphire

Sapphire is the mineral corundum, the same material as ruby, and the blue colour comes from traces of iron and titanium. This stone was mined in Sri Lanka, whose gravel beds have produced fine sapphires for more than two thousand years. Look at how the cutter has kept the stone deep, with a large flat table on top and many small facets around the sides and underneath: with a gem this big the aim is to hold the colour and weight rather than to chase the flashing brilliance of a small stone. The diamonds around it total about sixteen carats, which would be a substantial jewel on their own but here look like a modest frame. The setting is silver and gold and was made to be worn, though wearing it must have been a considerable effort.

The brooch belonged to Rebecca Pollard Guggenheim, who received it from her first husband, Colonel Robert Guggenheim, and after his death she married John Logan and gave the sapphire to the Smithsonian in 1960 under the Logan name. It joined the national gem collection two years after the Hope Diamond and has helped make the hall one of the greatest gem displays in the world. Notice the tiny inclusions visible with a close look, needle-like crystals that are natural fingerprints and one of the ways gemmologists prove that a stone came from the ground rather than a laboratory.

Did You Know? At nearly four hundred and twenty-three carats, the sapphire is roughly the size of a hen's egg and weighs almost ten times as much as the Hope Diamond.