Quarry Southern Africa November 2018 | страница 23

WINNING
‘interesting’ couple of months.
“As to the future I believe that we are in
for a very tight three years or so, before we
see an improvement in the construction
industry.”
He describes the primary challenge to
the ready-mix concrete business as being
one primarily of saturation of the market.
“There are so many players competing for
a pie which is shrinking, and as a result
the price of ready mixed concrete is being
driven down. Ready-mix concrete, as much
as aggregate, is a highly cut-throat business
which comes down to very tight margins,
requiring operators to run a tight ship,”
says Mandass.
Strerkspruit’s ready-mix plant makes
product to client specifications. The
concrete industry has evolved a long way
from where it used to be, and Mandass
says it [concrete] “can do some weird
and wonderful things today.” Coloured
concrete is an example of such an
evolution, he says, “The colourant added
is very expensive, but the final product is
beautiful for a commercial driveway for
instance. This is very technical because
if you lay a colour down it needs to be
consistent.” Quartzite is mined and used to manufacture glass, ferrosilicon, manganese ferrosilicon, silicon
metal, silicon carbide and other materials.
What is quartzite? plate boundaries. There, sandstone is
metamorphosed into quartzite while
deeply buried. Compression at the plate
boundary fold and fault the rocks and
thicken the crust into a mountain range.
Quartzite is an important rock type in
folded mountain ranges throughout
the world.
When the mountain ranges are worn
down by weathering and erosion, less-
resistant and less-durable rocks are
destroyed, but the quartzite remains. Wise
geologists won’t hit quartzite hard with a
rock hammer. If they do, they will make
sure they are wearing impact-resistant
goggles, gloves, long sleeves, long pants and
sturdy shoes. A sharp hammer blow usually
bounces off, sometimes causing injury.
When the rock does break, the impact
often yields sparks and sharp pieces of rock
travelling at high velocity.
Quartzite is a metamorphic rock composed
almost entirely of quartz. It forms when
a quartz-rich sandstone is altered by
the heat, pressure and chemical activity
of metamorphism. These conditions
recrystallise the sand grains and the silica
cement that binds them together. The result
is a network of interlocking quartz grains of
considerable strength.
The interlocking crystalline structure of
quartzite makes it a hard, tough, durable
rock. It is so tough that it breaks through
the quartz grains rather than breaking along
the boundaries between them. Quartzite is
usually white to grey in colour. Some rock
units that are stained by iron can be pink,
red or purple. Other impurities can cause
quartzite to be yellow, orange, brown, green
or blue.
Its extreme toughness made it a favourite
rock for use as an impact tool by early
man. It could be shaped into large cutting
tools such as axe heads and scrapers,
though its coarse texture made it less
suitable for producing tools with fine
edges such as knife blades and projectile
points. Most quartzite forms during
mountain-building events at convergent
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Uses of quartzite
Quartzite has a diversity of uses in
construction, manufacturing, architecture
and decorative arts. Although its properties
are superior to many currently used
materials, its consumption has always been
low for various reasons. In architecture,
marble and granite have been the favourite
materials. Quartzite, with a Mohs hardness
of seven along with greater toughness, is
superior to both in many uses. It stands up
better to abrasion in stair treads, floor tiles
and countertops. It is more resistant to most
chemicals and environmental conditions. It
is available in a range of neutral colours that
many people prefer. The use of quartzite in
these uses is growing slowly as more people
learn about it.
Quartzite’s soundness and abrasion
resistance are superior to most other
materials. Unfortunately, the same
durability that makes quartzite a superior
construction material also limits its use.
Its hardness and toughness cause heavy
wear on crushers, screens, truck beds,
cutting tools, loaders, tires, tracks, drill
bits and other equipment. As a result,
the use of quartzite is mainly limited to
geographic areas where other aggregates
are not available.
Quartzite is valued as a raw material
because of its high silica content. A few
unusual deposits have a silica content of
over 98%. These are mined and used to
manufacture glass, ferrosilicon, manganese
ferrosilicon, silicon metal, silicon carbide
and other materials. 
QUARRY SA | NOVEMBER/DECEMBER 2018_23