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There are time implications associated with the crystal sizes in igneous rocks - but
how much time? Dowty (1980) cites maximum rates of crystal
growth in a granite melt with 3.5% water as:
quartz 1.0 x 10^-8 cm/s
alkali feldspar 1.0 x 10^-7 cm/s
plagioclase 1.0 x 10^-6 cm/s
(Note: dry granites have higher growth rates).
The number of seconds in 1 year is 3.15 x 10^7. When compared
with the maximum growth rate parameters for wet granitic melts,
there are implications for time: large crystals need not imply
time intervals much greater than a single year. Luth (1976)
"It is frequently assumed that the presence of large
crystals in these phases implies slow growth over long periods
of time. Although this may be the case, the intent here is to
demonstrate that it does not necessarily hold" (p.405).
Of course, it is not our intent to suggest that any, all or most crystallization of granites or any other rocks necessarily occurred in one year.
Dowty, E. 1980. Crystal growth and nucleation theory and the
numerical simulation of igneous crystallisation. In: Hargraves,
R.B. (ed). Physics of magmatic processes. Princeton University
Press, New Jersey.
Luth, W.C. 1976. Granitic rocks. In: Bailey, D.K. and
MacDonald, R. (eds). The evolution of the crystalline rocks.
Academic Press, London.