Presumably what gvhst means is "It's useful gold is dense, as if there were cheaper denser metals you could create fake gold bars by gold-plating alloys of equal density"

After all, you can already get gold-plated tungsten bars [1] from companies like chinatungsten as 'novelty paperweights' [2] - even though tungsten is fractionally less dense than gold.

As iridium and osmium are traded in very low volumes and toxic/acidic, platinum is more expensive than gold, and tungsten is fractionally lighter, fake gold is seldom undetectable.

[1] https://www.google.com/search?q=tungsten+gold+bar&tbm=isch [2] http://www.paper-weight.cn/products-show.html