Heliodor is the yellow to greenish-yellow variety of beryl, coloured by iron, its name from Greek helios, sun, and doron, gift, the gift of the sun. It shares the beryl family properties of hardness 7.5 to 8 and hexagonal prismatic crystals, and it grades into golden beryl on one side and into green aquamarine on the other, the boundaries being matters of trade convention rather than sharp mineralogical lines. Fine heliodor came notably from Namibia and from Ukrainian and Brazilian deposits. Because it was distinguished and named only in the early twentieth century, heliodor carries no ancient tradition, and older references to yellow gems are as likely to mean topaz, citrine or chrysoberyl. Its modern metaphysical associations, generally solar, warmth, vitality, the solar plexus, follow directly from the golden colour and the name and belong to recent crystal practice.
The beryl family, of which heliodor is a member, left an unexpected mark on everyday language: German Brille, spectacles, descends from Latin beryllus by way of Middle High German berille, because the earliest eyeglass lenses, ground in the thirteenth century, were made from clear beryl before glass-grinding improved enough to replace it. Gem-grade yellow beryl is mined today chiefly in Brazil, Namibia, where it comes from the same pegmatites as blue aquamarine, and Madagascar, and because the variety was named and separated from plain golden beryl only in 1910, references to a yellow beryl gem before that date cannot be assumed to mean this specific stone rather than citrine or topaz.