EHRC Homepage | New Category | Your Questions

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) comments:

"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.

______________________________________________________ Ó 2010 Arthur V. Chadwick, Ph.D.