A large naturally black diamond has gone on display in the Natural History Museum’s minerals vault after being loaned to the museum for a year.
All diamonds are coloured by impurities in the crystal, but a pure black diamond is quite unusual as only one in 10,000 natural diamonds is classed as fancy coloured, and out of these, only a handful of them are truly black. In addition to being unusual in colour, at 93 carats, it’s also the largest diamond currently on display at the Museum. The Museum currently holds three black diamonds in its collections, but all are substantially smaller.
Named by the unnamed owner after his daughter, the “Anastasia Diamond” was cut from a rough diamond weighing just over 300 carats, which likely originated from Brazil. The rough was acquired by the lender’s family during the late 1800s in Goa, India which was well known as a gem cutting centre at the time, and the gemstone has remained with the family since.
The diamond was later set into jewellery as a pendant for the lender’s daughter, after whom it is named. The piece is inspired by Arabic culture and symbolism. It includes a large crescent moon, and on the rear of the pendant is a depiction of the constellation Al-Dubb al-Akbar, otherwise known as Ursa Major, in diamonds.
The black colour in diamond has several causes. Many, and including this one, are formed of tiny intergrown crystals known as polycrystalline. They also contain nano- to micro-sized inclusions of minerals such as graphite, and internal fractures. These inclusions make the cutting and polishing of the gemstone and achieving the mirror-bright lustre much more challenging. The tiny interlocking grains can be seen as lines on the surface of the polished faces. The diamond is translucent rather than opaque, and the inclusions can be seen as scattered ‘glitter’ within.
The Black Diamond is currently on display in The Vault, a secure space at the far end of the Mineral’s gallery alongside a selection of gems and minerals including the recently discovered Winchcombe Meteorite.
The black diamond will be on display until October 2022.