The γ polymorph forms at temperatures below 500 °C through
the β→γ conversion [17]. This conversion involves a rotation of the
SiO4 tetrahedra and large movements of calciumatoms [20]with an accompanied
volume increase of 12% causing a break up into small
particles, a phenomenon known as “dusting” [17,21,22]. It is known
that the β→γ conversion can happen during or long after the cooling
[22], as well as that it can be stress-induced e.g. by grinding [17]. It is
also known that the β → γ conversion can be suppressed by rapid
cooling and/or by addition of suitable dopant ions such as boron [7].