Splitting Basalt

[Simon Brown <moonsong@zzzzzzzzzzzzzzz>]

Hi Calvin,

The secret is in the different mineral makeup of granite compared to basalt.
Granites are composed of a range of minerals with differing sizes of grain,
while basalts (and many other stones) are made up of largely one mineral
type, all roughly the same size.

When granite is heated, some minerals (mica) expand really quickly and force
the other minerals apart. When there is only one size, they heat and expand
fairly equally.

The difference in expansion caused by heating of different minerals makes
the granite flake off: "exfoliation". Basalt will do this as well, but not
as spectactularly as granite.

Simon