Black Crystals Explained | Crystal Vaults
To form a black gold alloy, gold is mixed with another metal such as cobalt, usually to the ratio of 3 parts gold to 1 part metal. However, although this is called an alloy it is not really one. The black layer is only on the surface unlike other alloys where the metals are combined.Gold often occurs in free elemental (native) form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the native element silver (as electrum) and also naturally alloyed with copper and palladium. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides).