planes in granite

["John Vancamp" <jvcstnwrks@zzzzzzzzzzzzz>]

 The picture
 (you can google similar ones) clearly shows the curved layers of the
 granitic dome. If granite were a huge
 perfect crystal I could see why there might be three planes, but it
 seems to be made of randomly arranged grains. Is this perception wrong?

Norman,

Those curved sheets of granite you see on the weathered granite domes are
an erosional feature call exfoliation.  Very common in granite.  Results
 from the surface heating and expanding during the day, and cooling back
down at night.  Enchanted Rock near Llano Texas got it's name from the
noise the dome makes during the cooling phase at night. Not much to do with
the actual "grain" structure of the stone, but rather the depth within the
stone the heating/cooling cycle can penetrate.

The other thing about the tree planes does have to do with the graining
developed during the cooling of the molten source material.  Grain
(crystal) size is a function of speed of cooling.  Slower = bigger.  But
that randomness you speak of is not entirely random as magnetic fields
effect crystal growth, orientation, and alignment, so what to the naked eye
may appear random actually has some structure.  In sedimentry stone, we
refer to vein cut, or bed cut,  which is parallel to deposition, and cross
cut which is across the plane of deposition.  Carvers love "free stone"
which works equally as well in either direction.  In the plutonic igneous
stone,  what would be the equivalent of the cross cut is in essence
effected by this crystal / grain orientation, in which the grain can be
aligned parallel to the line of cut in one direction but against the line
of cut in the right angle direction, both parallel to the bedding.  Bedding
in this type of stone is not a depositional feature, but representative of
the cooling process.

Igneous stone are so much more complicated and complex than the sediments I
am most familiar with.  I didn't pay too much attention during the one
petrology class I took as my interests even then where elsewhere.  So I
hope I'm close here, and haven't muddied up the magma pool too much.

JVC