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Posted on 17/01/2014

Contributed by

Helen Maynard-Casely

GOLD! The crystal structure of success

What does it look like?

Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

What is it?

It's coveted by many, yet owned by very few but on a crystal structure level gold is actually very similar to quite a few other metals. At this level the gold atoms can nearly be thought of as spheres. The structure of gold can be described as cubic close packed – or face centred cubic. Each edge of the cube is 4.07 Å long. You can see from the image above that the basic building block of the structure, with an atom of gold at each corner and sitting in the middle of each face. This is one of the most efficient ways that spheres can pack together, using 74 % of the space.Other metals that form the same crystal structure are Platinum, Lead, Nickel and copper.

Gold is the ultimate play-doh. It's relatively soft but is also very very malleable, a 1 gram amount can be beaten into a one meter square sheet. Gold's softness is one of the reasons why it can collect in fluvial beds to form beautiful flowing nuggets. This relationship with water means that gold can even get sucked up into leaves of eucalyptus trees. Australian scientists last year showed that trees in gold mining areas can suck up gold into their leaves, which means checking the leaves could be a cheaper way to hunt for the gold below.

Where did the structure come from?

Though it was pretty well known that the structure of gold was face centred cubic, a paper by Jette and Foote determined very accurately the length of the cubic for a number of materials – including gold. This was very important work, because of the use of Gold and similarly unreactive metals as standards in lots of experiments. This crystal structure is #9012430 in the open crystallography database.

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