Repeated with slight verbal variation at chi 52.
The headword h)/lektron, a neuter noun, means two things (see LSJ s.v.): (I) amber, the fossilized resin from pine-trees, known for its static electric properties; and (II) -- the meaning relevant to this entry -- a ternary alloy of gold, silver and copper. The Greeks recognized two types of alloys, one known as leuko\s xruso/s and another known as electrum/elektron, an artificial alloy of gold, silver and copper, often used in Greek coins. The electrum alloy is much harder than gold or silver. Pliny (Natural History 33.80) says "all gold contains silver in various proportions ... Wherever the proportion is one-fifth, the ore is called electrum." This does not necessarily mean that electrum was an alloy of four parts of gold and one part of silver, but rather that any gold with a 20% silver content should not be classified as gold. Compare Isidore, Origines xvi, xxiv.
[1] Same glossing in Hesychius eta334.
[2] Same glossing in Photius (Lexicon eta111) and elsewhere. The explanation perhaps concerns inlays in the famous altar: see next note. The term u(elo/s means some kind of crystal, rock crystal or glass (see upsilon 6, upsilon 74).
[3] In Constantinople; cf. sigma 809.