The gold coins on Harn, Lythia, and Kelestia are either made out of gold or silver. They are either called gold penny, gold pence or gold piece. Most commonly it is called gold penny. The silver coin that is equivalent to the gold pence (1 gp = 20 sp) to is also called gold piece/gold penny or gold pence.
The golden coin is similar to Guatemala Gold Four Reales 1860, a tiny 9mm coin. Below are pictures of this coin:
The dimension are as follows: 9mm in diameter, and weighs 0.83 grams. And the coin is 2mm thick.
Typically, there are between 546 to 533 coins to a pound.