Complex sentence: Croesus is credited with issuing the first true gold coins with a standardised purity for general circulation.But they were quite crude, and were made of electrum, a naturally occurring pale yellow alloy of gold and silver.
Split into simpler sentences: Croesus is credited with issuing the first true gold coins with a standardised purity for general circulation. However, they were quite crude, and were made of electrum, a naturally occurring pale yellow alloy of gold and silver.