The Millbillillie eucrite belongs to one of the rarest meteorite types. It is part of the HED group, which also includes howardites and diogenites. Eucrites are achondrites, meaning "not chondrites," so they are lacking in chondrules—the small, spherical, pre-solar grains that give the common chondrites their name. Millbillillie meteorites are volcanic rock from other worlds, and are comprised largely of silicate minerals. They are light in weight—similar in feel to terrestrial pumice—and are among those extremely uncommon meteorites which contain no iron, and show no attraction to a magnet. As such, they are less dense than the majority of meteorites and even a modest specimen of 6 or 7 grams can still be enjoyed and studied without magnification.