Ronnie Bennett, age 10, of Peterboro, Ontario, Canada, for his question:

What sort of mineral is feldspar?

 

The word feldspar means fieldstone, but we find it everywhere    in fields and forests, mountains and valleys, deserts and prairies. In fact, fieldstone is the most plentiful mineral we have. About 60 per cent of the earth's igneous rocks are feldspar of one sort or another. The mineral is a silicate, a compound of three atoms of silicon and eight atoms of oxygen, plus one atom of aluminum. Chemically it is a friendly compound, willing to adopt atoms of other elements, and the basic compound may include sodtum, potassium or calcium.

This is why we have so many varieties of feldspar. If you are a rock hound, many of your specimens may be different forms of this hard, heavy mineral. The rough stones often range from pasty whites to pale grays, sometimes tinged with rusty pinks. Glossy moonstone is crystal feldspar and waxy labradorite is a peacock blue crystal form of the same everyday mineral. Its crystals also occur in pastel blues and greens and chocolate browns.