Is My Countertop
Quartzite or Marble?
By Frederick M.
Hueston
In recent years, there have been complaints from consumers who purchase
countertops from stone distributors who tell them the material is quartzite,
which will not etch (a dullness of the surface) or scratch. Later, when their
tops are etched and scratched, they learn the hard way that their tops are
actually marble. This article explains the difference between quartzite and
marble so that consumers can tell what countertop material they truly have.
About
Marble
Marble is a
metamorphic material that contains an abundance of the mineral calcium
carbonate, which is soft and chemically reacts to acidic substances. This means
marble is very susceptible to acid etch damage. Heat, pressure, and other
geological forces destroy or modify the texture and structure of limestone or
dolomite rock, resulting in a new form of rock known as marble. When the
limestone or dolomite are very pure, the resulting marble is white. When the
quartz is mixed with iron oxide or other minerals, the resulting quartzite may
have streaks, lenses (transparent pieces), and varieties color.
About
Quartzsite
Quartzsite is also a
metamorphic rock but differs from marble in that it does not contain calcium
carbonate. This means it is not susceptible to acid etch damage. Quartzite is
formed when heat, pressure, and other geological forces destroy or modify the
texture and structure of quartz sandstone. When the quartz sandstone is very
pure, the resulting quartzite is white or gray. When the quartz is mixed with
iron oxide or other minerals, the resulting quartzite may have streaks, lenses,
and varieties color.
Tests
to Determine Stone Type: Marble or Quartzite?
Marble and quartzite can be very similar in appearance. Fortunately, there are
a couple of simple tests one can perform to tell the difference between marble
and quartzite: the scratch test and the acid test. If you attempt to perform
either of these potentially destructive tests, you should obtain a sample or
use a piece of scrap countertop material to perform the tests. If neither are
available to you, test in an inconspicuous spot knowing that the test may cause
damage.
The Scratch Test
In order to understand how the scratch test works, we need to provide a little
more science. The hardness of minerals can be determined by what is called the
Mohs scale of mineral hardness. This scale rates minerals from the softest
mineral, being a 1, to the hardest mineral, being a 10. Calcium has a Mohs
hardness of 3. Quartz has a hardness of 7. A standard kitchen knife has a
hardness of about 6.
Use a knife to scratch the surface of a countertop. The outcome indicates the
hardness of the mineral. If the knife leaves a scratch, the stone is likely
marble. If there are no scratches, the stone is likely a much harder stone like
quartzite or granite.
The Acid Test
Calcium reacts to acids, causing etch damage. The etch may or may not have
texture, depending on the severity of etch damage. Common acids will not affect
quartz. Vinegar or a lemon wedge can be used for the test. Place the lemon
wedge or a drop or two of vinegar on the stone and allow several minutes dwell
time. Wipe up the excess. If it leaves a dull spot, that a positive indication
for the presences of calcium, which indicates the countertop is marble and not
quartzite.
Uh-Oh,
It's Marble
If you discovered you have marble, not
quartzite, by way of these tests or because you already have countertops
installed that have etch marks or scratches, rest assured that you are not
doomed to live with unsightly damage or replace your countertops. Professional
stone restoration contractors can hone and polish your countertops, virtually
erasing damage and leaving your tops with a beautiful, pristine finish. Your
contractor can also make recommendations for care and protection appropriate
for your countertop material.
It is unfortunate that marbles are being sold as quartzites. While they can
look similar, they do not react the same. If you are in the market for new
countertops, these tests can help you make an informed decision on your
investment.