Boyd’s Bible Dictionary:
Hardly the fossil vegetable gum of commerce (Ezek. 1:4,27; 8:2); but rather the yellow composition of gold and silver known as electrum.
Concise Bible Dictionary:
This probably refers, not to the mineral now called “amber,” which is highly electric, as its Greek and Latin names imply ἥλεκτρον, electrum; but to a mixed metal, such as the ancients described as composed of four parts of gold and one of silver. The Hebrew word is chashmal, and is associated with fire, and refers simply to its color and brightness (Ezek. 1:4, 27; Ezek. 8:2).