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Q - Pebbles are more likely to be igneous rocks than sedimentary
or metamorphic. Why?
A - Igneous rocks are much harder than the two other kinds and
so do not wear away as easily.
Q - Though most of the rocks in the world are of three types -
sedimentary, metamorphic and igneous, there is a fourth type. What
is it?
A - Meteorites which fall out of the sky. About 10, 000 tonnes
per year in fact. Most of it is dust, but about twenty samples weighing
more than 1kg strike the Earth too. The Moon's heavily impacted
surface probably indicates that Earth has been struck with the same
regularity. However, weathering on Earth may have eroded many of
the craters. Some do survive however, including Meteor crater in
Arizona, USA, which was made by a meteorite about 100m wide!
Q - Name a famous example of an unusual basalt formation.
A - The Giant's Causeway in Northern Ireland, with its thousands
of six-sided columns.
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