Epilogue - Thanatia: The Destiny of the Earth's Mineral Resources - page 503

For a specific mineral, “natural rarity” refers to favourable composition, concen-
tration or degree of cohesion - a set of conditions which are extremely di cult to
find. “Technological rarity” meanwhile, relates to the costs associated in bringing
minerals from mine to market conditions. If one considers all these characteristics
from a thermodynamic perspective, they are all rooted in entropy. The dispersion
and mixing of materials are principally the results of geological forces moved by
both the sun and the Earth's internal heat over millennia, where the effects of the
Second Law become evident.
Exergy is a measure of the degree of thermodynamic distinction and in this
sense it is a measure of an object's rarity. Something other than commonness is
rare, and the rarer something is, the greater its distinction. It is therefore not
surprising that “thermodynamic rarity” is stated in exergy terms. Consequently, a
mineral's thermodynamic rarity has been defined in this topic as “the amount of
exergy resources needed to obtain a mineral commodity from bare rock”. Notwith-
standing for this definition to be complete, one needs to specify the reference state
from which distinction is measured and the technology one is currently using. Ac-
cordingly, a mineral's thermodynamic rarity is more precisely defined as “the actual
amount of exergy resources needed to obtain a mineral commodity from Thanatia
to the prefixed commercial conditions using the current best available technologies”
(Sec. 4.5). Rarity thus becomes a quantifiable thermodynamic property measured
in kJ. Thermodynamic rarity is composed of two complementary parts: the natural
bonus, which is a hidden cost and the “OTR” costs, i.e. the actual amount of re-
sources needed to convert a mineral into a commodity via extraction, beneficiation,
smelting and refining.
The probability of finding new deposits is decreasing due to human activity.
Hence, rarefaction is a Man-induced process. In the technosphere, it appears at
the mineral's beginning-of-life (BoL) and at its end-of-life (EoL). In the former,
as mining continues and ore grades decline, the operation becomes ever costlier.
In the latter, rarefaction occurs when materials become dispersed into Thanatia.
Consequently, the rarefaction process carries two costs, one at the BoL and the other
at the EoL. Thermodynamic rarity has a bearing on global energy consumption
and the sustainability of planetary resources because the greater the rarity, the more
di cult it is to obtain a given commodity.
It is worth remembering that if technology does not change the thermodynamic
rarity of a given mineral will remain constant 4 . It is a property of a given mineral
reflecting its natural scarcity or abundance and the relative technological di culty
or ease in obtaining it. This is because the mineral wealth of the Earth (at least for
the non-fuels) is in fact constant. It is either in the geosphere or in the technosphere.
Before the appearance of any mining activities, all geological heritage remained in
the geosphere, in the form of very concentrated mineral deposits. At that point
4 As explained in Sec. 4.5, this is a simplification because in reality the exergy replacement costs
do not vary lineally with the ore grade.