The demon Gemmos appears in the grimoire The Book of Oberon
From The Book of Oberon, Dan Harms edition:
Gemmos, a stronge lord, appeareth like a knight, his horse is red, & he speaketh with a strong voice, & he teacheth howe all kind of mettals, maye be turned into, pure gold, & he knoweth the vertues of hearbes, & precious stones, & he teacheth phisick logicke, & giveth true aunswere of thinges stollen, & he was of the order of the Archangels, & therfore he is of the greater force, & hath under him 27 legions.
This demon was of the angelic order Archangel
Timeline of related events
1577Book of Oberon completed (lists this demon)