THE THIRD PLANET
E. R. SWANSON – spring 2009
While anthropologist go to great length and archeologist go to great depths to
study Stone Age people, in many ways modern humans have never left the Stone Age.
The fact is that people today use far more stones than did our ancient ancestors; we just
use the more modern sounding term of industrial minerals.
Industrial minerals are
nonmetallic rocks and minerals, typically consisting of low-value materials used in
large amounts, mostly by industry
(hence the name).
Industrial minerals have
essentially very little value.
Their price mostly reflects the cost of mining, processing
Industrial minerals are usually abundant and widespread and
typically mined to satisfy a local demand.
A few examples include: crushed rock,
building stone, sand and gravel, cement, asbestos, salt and the minerals constituents of
Sand and Gravel
Sand and gravel are essential construction materials.
Sand and gravel are typical
extracted from stream beds where nature has already done most of the work by breaking
up the material and sorting according to size.
Sand and gravel may be combined with
cement to make concrete, a commodity with a more interesting history.
Ancient Greek buildings were constructed with blocks piled on top of other
Cement was a later Roman invention.
You can see how the Romans used
cement in the mortar holding bricks together in the Coliseum at Rome.
But whoever was
put in charge of writing down all the knowledge as Rome fell and European intellectual
lights went out during the Dark Ages, must have forgotten to include the formula for
The recipe was rediscovered centuries later, in 1824, by Englishman,
Joseph Aspidin, who patented the formula for what is called Portland cement.
Apparently, the artificial rock that Aspidin made just happened to look a great deal like
Portland Stone, a rock quarried and used in the day, and the name Portland stuck to the
The recipe for Portland cement starts with
), a good source for
the lime (Ca0) that cement needs and cement’s major ingredient by a factor of ten.
should be no surprise, then, that cement plants are located next to limestone exposures
near big cites.
San Antonio has had its share of limestone quarries over the years.
you drive away from the city you pass abandoned limestone quarries that have been left
behind for the bears at the City Zoo, for students at Trinity University, shoppers at The
Quarry and La Cantera (Cantera means quarry) and thrill seekers at Fiesta Texas.
Cement also needs a source of alumina (Al
) and silica (SiO
), and the sedimentary
materials typically used for this purpose are
shale or clay
It would be beneficial for
cement economics if the cement plant was located next to limestone interlayered with
shale at about a ratio of 1 part shale to 9 parts limestone.
Although other ingredients