Bdellium refers to something in pieces, many pieces:  gum, of course, sticks together; whereas, pearls are hard and do not stick together.   Thus, bdellium refers to many pieces with different qualities.   Bdellium is an adjectival noun, a specific noun that describes itself.

          For example, speaking of a group of people, one could say, "The bdellium went to the Temple to pray."   Or, "The bdellium on board Noah's ark included both children of Adam and children of Cain."   "The local zoo is a bdellium of birds, animals, reptiles, people, etc."   A bdellium even describes a used vehicle sales lot containing a potpurri of vehicles (the good and bad; new and old; cars, vans, and trucks; makes and models; etc.).   A gravel pit could be described as a bdellium of stones, sand, and whatever.   Note:  A pile of crushed stone or sand, for example, could not be termed a bdellium as each particle has the same qualities that don't change.

          Numbers 11:7 speaks of manna as like coriander seed, the color (resemblance) of bdellium.   Here bdellium refers to something like rice (whole grain, unbleached rice) ... many particles of hard material (uncooked); whereas, the cooked is soft and gummy.   Again, there are many particles and different qualities.

          Genesis 2:12 refers to bdellium and to the onyx stone in reference to the Edenic Valley, in the land of Havilah, which contained many people of different qualities (i.e. the obedient and disobedient, male and female, young and old, tall and short, fat and skinny, learned and unlearned, strong and weak, rich and poor, etc.).

          People, as described by bdellium, stick together in families, groups, communities, cities, and nations (islands of humanity); whereas, the onyx refers to a harder stone, a chalcedony of crystals of different colors blended together yet separate.   So, Genesis 2:12 uses both bdellium and the onyx to describe people that dwelt in Eden:  the Little Flock versus the Great Multitudes, the more obedient versus the disobedient.