1. METALLIC MINERALS. These include things most of us would think
of if we were asked to name some minerals. Familiar examples are
copper, silver, mercury, iron, nickel and cobalt. Most of them are
found in combination with other things--as ores. We get lead from
galena, or lead sulfide. Tin comes from the ore cassiterite; zinc
from sphalerite and zincblende, or blackjack. Chromium that makes
the family car flashy comes from chromite. Many minerals yield
aluminum. Uranium occurs in about 50 minerals, nearly all rare.
Twenty-four carat gold is a metallic mineral. A 14 carat gold ring
contains 14/24 or 58% gold.

An average sample of earth contains 9% aluminum, 5.5% iron, .01% zinc,
.008% copper, .004% tin, .002% lead, .0005% uranium, and .0000006% gold
or platinum. It would be hopelessly expensive to recover such metals
from an average ton of earth. That's why metallic minerals are taken
from concentrated deposits in mines.

Many valuable minerals are found in veins running through rock. Veins
can be formed when: (a) mineral-laden ground water seeps into cracks,
evaporates, and leaves mineral grains that build up into a vein;
(b) hot water from deep within the earth fills cracks, then cools
and deposits much of the material in solution as minerals in a
vein--sometimes including metals such as gold and silver; (c) molten
gaseous material squeezes into cracks near the earth's surface,
then slowly hardens into a vein.

2. NONMETALLIC MINERALS. These are of great importance to certain
industries. You will find them in insulation and filters. They are
used extensively in the ceramic and chemical industries. They include