Geology Reference
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requires energy to be transferred by means of heat into
the crystal from the 'surroundings' (the air or water
surrounding the crystal). The crystal experiences an
increase in its internal energy, which transforms it
into  liquid water. The process can be symbolized by
writing down a formal reaction:
The purpose of this topic is to introduce the average
Earth science student to chemical principles that are
fundamental to the sciences of geology and environ-
mental geoscience. There can be no more fundamental
place to begin than with the topic of energy (Box 1.1),
which lies at the heart of both geology and chemistry.
Energy plays a role in every geological process, from
the atom-by-atom growth of a mineral crystal to the
elevation and subsequent erosion of entire mountain
chains. Consideration of energy provides an incisive
intellectual tool for analysing the workings of the com-
plex geological world, making it possible to extract
from this complexity a few simple underlying princi-
ples upon which an orderly understanding of Earth
processes can be based.
Many natural processes involve a flow of energy.
The spontaneous melting of an ice crystal, for example,
in which molecules of water (H 2 O) are represented as
migrating from the solid state (left-hand side) into the
liquid state (right-hand side). Even at 0 °C, ice and
water both possess internal energy associated with the
individual motions of their constituent atoms and mol-
ecules. This energy content, which we loosely visualize
as heat 'stored' in each of the substances, is more cor-
rectly called the enthalpy 1 (symbol H ). Because the
Words in bold type indicate terms that are defined in the
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