Final answer:
The least valuable gem, if value was based solely on abundance, would be air, as it is supplied in vast quantities at no cost. While air is not a gem, it exemplifies the principle that abundant items are considered to have lower value, much like a hypothetical, mountain-sized diamond would drastically reduce the value of diamonds due to its abundance.
Step-by-step explanation:
If abundance at the surface of the earth were the only measure of value, air would likely be considered the least valuable gem. Gems are typically valued for their scarcity and beauty, and while air is not a gem, it can be compared metaphorically in terms of abundance. Just like the liberally available air we breathe, items that are plentiful and can be easily accessed or produced would not garner high value. This is based on the economic principle that abundance can lead to lower value.
Correspondingly, the extreme scenario described where a diamond as large as a mountain exists suggests that if such a diamond were to be introduced into the market, it would drastically reduce the value of diamonds due to overwhelming abundance. This fictional example illustrates how even diamonds, ordinarily considered valuable, could become virtually worthless if they were too abundant.
In contrast, scarce resources, such as unique stones that require laboratory analysis to verify their extraterrestrial origins, are considered valuable especially when they are collected in pristine condition. This rarity and the conditions of their retrieval add to their value. Thus, abundance indeed significantly influences the perceived value of an item, be it air, common stones, or theoretically, expansive diamond reserves.