GemStone III has at least as many different types of materials in it as exist on Earth because everything from iron and steel to oak and yew can be found there. Where it gets more interesting is in the different magical materials that exist. Originally, these materials had names taken directly from Iron Crown Enterprises' "RoleMaster" gaming products.
Until 1998, ICE had the worldwide gaming rights to the Middle-Earth world-setting created by J.R.R. Tolkien. The names that he created--mithril, eog, galvorn, and others--are therefore found throughout ICE's gaming products.
When GemStone III was written, the names of these materials were used but the properties of them were not necessarily copied over as well. For example, in "RoleMaster" the material eog has a +30 magical bonus; in GemStone III, eog is only +10.
At the end of 1995 when the ICE age came to an end, Simutronics was legally required to change all references to materials with "RoleMaster" names. Items actually in the possession of characters were allowed to retain their old material names, with the stipulation that should the item ever be handled by a GameMaster, the material would be converted to whatever the corresponding new material was called. (For example, an old "galvorn" item that a GameMaster needed to work on for some reason would be returned to the player as a "golvern" item.)