The Quartzite Quandary

After years of hearing from disappointed clients about their “quartzite” etching, we thought it was time to clear things up.

First Encounters

Many years ago, when the company was first getting started, our experience with quartzite was limited to the occasional service call—filling a chip, touching up silicone or cleaning around faucets. At the time, quartzite was still a relatively rare material for us to encounter. It was always a treat to see this heavily veined stone that could look remarkably like marble while behaving more like a much harder material.

As on-site restoration specialists rather than fabricators, we aren't exposed to every variety of stone passing through local suppliers, and at that point we had very little experience actually resurfacing quartzite. Then came what we still call “the first Muskoka job”: a wall-to-wall slab installation in a beautiful cottage, sold as Super White quartzite.

When we arrived to assess the installation and begin our mitre work, we were a little intimidated. True quartzite can be exceptionally hard and demanding on diamond tooling, and we expected it to test the limits of our discs. We aren't geologists, mineralogists or scientists, but after decades of grinding, sanding and polishing stone, you develop a pretty good feel for how different materials behave under an abrasive.

Once we started sanding, something immediately seemed wrong. I called the installer and said, “There’s no way this is quartzite—this has to be marble.” It was cutting far too easily compared with what we expected from true quartzite. They insisted it was quartzite, and we agreed to disagree.

Superwhite "quartzite"

The Phonecalls

After that first major “quartzite” job, the phone calls started coming more frequently. Clients were contacting us about etches, stains and scratches on countertops they had purchased as quartzite. Many told us they had been assured the material would be etch-proof, harder and more durable than granite, and highly resistant to staining. Yet some of the countertops we were seeing clearly weren’t behaving that way.

The conundrum on our end was figuring out how to restore them. The material was noticeably harder than the average marble under diamond abrasives and, in some ways, behaved more like granite. At the same time, we were looking at rings, dull spots and acid etches—the kind of damage we normally associate with marble and other calcite-based stones.

We experimented with both marble and granite restoration techniques until we found combinations of abrasives, compounds, pressure and speed that produced consistent results. Even now, the exact approach often needs to be adjusted from one variety to another. We had figured out how to restore the material, but we still had one fairly obvious question:

What exactly were we working on?

Dolomitic Marble

At this point, we started to suspect that the material we were seeing simply wasn’t quartzite at all. We had now worked on true quartzite, and the difference in the way these other “quartzites” cut, polished and reacted to acids was becoming difficult to ignore.

Marble and quartzite are both metamorphic stones, formed when existing rock is transformed by heat and pressure. What separates them is largely their mineral composition. Traditional marble is composed primarily of calcite, a form of calcium carbonate. Quartzite, on the other hand, is composed predominantly of quartz. That difference is enormous from a restoration standpoint: calcite is relatively soft and reacts readily with common acids, while quartz is much harder and far more chemically resistant.

Then there is dolomitic marble. Instead of being composed primarily of calcite, it contains a high proportion of the mineral dolomite—calcium magnesium carbonate. Dolomite is somewhat harder and generally reacts more slowly with weak acids than calcite, so dolomitic marble can behave noticeably differently from conventional marble. It is still an acid-sensitive carbonate stone, however, and it is nowhere near quartzite in hardness.

This explained much of what we had been seeing. Some materials being sold commercially as “quartzite” were actually dolomitic marbles: harder and sometimes more etch-resistant than typical marble, but still capable of developing the rings and dull spots our clients were calling us about. To complicate things further, marble, dolomitic marble and quartzite can have remarkably similar colours, veining and movement.

Appearance alone is not a reliable way to tell them apart.

The first image shows a dolomitic marble that was sold as “quartzite.” While somewhat harder than conventional calcitic marble, it remains susceptible to etching and other forms of wear. The second image shows true quartzite, a highly durable material composed predominantly of quartz and generally much harder than marble. Note how similar the two stones can appear despite behaving very differently in use.

Above: Hardness scale showing the difference in hardness between marble, dolomitic marble, granite and quartzite

True Quartzite

True quartzite is an exceptionally hard and durable natural stone. Because it is composed predominantly of quartz, it is highly resistant to scratching and abrasion and does not react to ordinary household acids the way marble and other calcite-based stones do. Porosity can vary from one quartzite to another, but many varieties are relatively dense and resistant to absorption when properly sealed where necessary.

That isn’t to take anything away from granite—it remains one of the most durable natural stones available. What makes quartzite unusual is the combination of durability and appearance. Many granites have a more granular or consistent mineral pattern, while quartzite can display dramatic movement and veining remarkably similar to marble. In some varieties there is even enough translucency for backlit applications, as shown below. You get much of the visual character people love about marble in a considerably harder, more acid-resistant material. Dare I say, it is a pretty impressive combination.

All of that does come at a cost. High-quality quartzite slabs can be expensive, and the hardness of the material creates additional challenges during fabrication. Cutting and shaping can be slower, diamond tooling wears more quickly, and extra care is required to avoid chipping or cracking the slab during fabrication and installation. Quartzite may be extremely hard, but like other natural stones it can still be brittle.

The payoff is a surface that, when correctly identified and properly installed, is exceptionally resistant to everyday wear. True quartzite is highly resistant to household acid etching, difficult to scratch under normal use and can perform for many years with relatively little restoration. From our perspective as restorers, one of the more telling observations is simply how rarely we receive calls about problems with genuine quartzite compared with the softer materials being sold under the same name.

Backlit translucent quartzite

How to Test Quartzite

If you’re unsure whether the material you’re buying is true quartzite or a softer stone such as dolomitic marble, there are a few simple tests you can perform yourself. These tests can help determine how hard the stone is and whether it reacts to acids—the reaction responsible for the dull spots and rings we refer to as etching.

The Scratch Test

Take a small sample or offcut of the stone you are considering and a piece of glass—wear eye and hand protection. Press a fresh edge of the stone firmly against the glass and drag it across the surface with moderate pressure. If the material is true quartzite, it should leave a definite scratch in the glass rather than simply leaving a removable mark on top of it.

Quartzite is hard enough to scratch ordinary glass. Calcite and dolomite, the primary minerals in standard and dolomitic marble, are not. If the stone cannot scratch glass, that is a strong indication that you are not dealing with true quartzite.

The Etch Test

Take a small sample or offcut of the stone and place a few drops of ordinary white vinegar on the polished surface. Avoid stronger cleaners or acids such as CLR. Allow it to sit for 10–15 minutes, then rinse the area thoroughly with clean water and allow it to dry.

Examine the surface under reflected light. True quartzite should show little to no reaction, while standard marble will usually develop a noticeable dull or etched spot. Dolomitic marble is less reactive and may show only a subtle etch. Used together with the scratch test, this can be a strong practical indication of what type of stone you are dealing with.

Work Gallery

In addition to our normal maintenance services, we also work alongside installers, completing colour matched epoxy mitres, crack and chip repairs and sealing.