· by Michael Blair, Nashville's Countertops
Quartzite has become one of the stones people ask for by name, usually because they want the look of marble with a harder surface. The trouble is that the name gets attached to more than one kind of rock, and it sounds close enough to quartz that the two get mixed up at the counter where you pick a slab. A quartzite top costs real money and is cut once. This is how we tell what a slab actually is before it goes on your cabinets, and what the answer means for how you live with it afterward.
Is quartzite the same thing as a quartz countertop?
No. Quartzite is a rock that comes out of the ground, and a quartz countertop is a slab made in a plant. Geology.com’s page on quartzite explains that it starts as sandstone rich in quartz and is changed by heat, pressure and chemistry deep underground, and it puts the stone at about seven on the Mohs hardness scale because of that quartz. The same page notes that it holds up well enough to be used for stair treads, floor tile and countertops.
A quartz countertop is engineered, a manufactured slab bound with resin, which is why its makers write their own care rules. Cambria’s care page warns that a hot pan set straight on its quartz can damage it and tells owners to use a hot pad or trivet, and its planning and care notes say it never requires sealing, polishing or reconditioning. Those rules belong to the manufactured product. They tell you nothing about a slab of quartzite, which is quarried, cut and finished the way granite is and sits with the other natural stone on our granite and natural stone page.
Why can’t I go by the name on the slab?
Because the names used in the stone trade are commercial, not geological. A slab’s name is chosen to sell it, often from its color or the place it was quarried, and nothing requires the word on the tag to match what a geologist would call the rock. Geology.com points out that in the dimension stone trade some quartzite is sold as granite, which shows how loosely the labels travel. A softer stone can just as easily end up in the quartzite row.
There is a technical standard behind the word. ASTM C616, the specification for quartz-based dimension stone, sorts these stones by their free silica content into three classes, sandstone, quartzitic sandstone and quartzite, and sets requirements for absorption, density, compressive strength, modulus of rupture and abrasion resistance. A label in a showroom does not tell you which class a stone falls in, or that anyone checked. So we treat the name as a starting point and look at the stone itself.
How do we check a slab before you buy it?
We test a sample piece of the stone rather than trust the label. A scratch test is ordinary trade practice and it is what we do first: a stone that is mostly quartz, at about seven on the Mohs scale, will cut into a piece of glass, and a softer stone will not. We also set water on the sample and watch whether the stone darkens, which shows how readily it takes in liquid.
The test only means something if the sample comes from the slab you are buying. The Natural Stone Institute’s comparison of natural stone and manufactured slabs notes that absorption can vary by stone type and by quarry source, so two slabs sold under one name can behave differently. That is one more reason we have you choose the actual slab, whether the kitchen is in Oak Hill or out in Spring Hill, and why the slab is laid out before it is cut, as we describe in templating and fabrication.
What we look at before a quartzite slab is cut:
- A sample piece from that slab, not a showroom chip
- Whether the sample scratches glass
- Whether water darkens the sample, and how quickly
- Where the veining runs, so seams and sink cutouts land well
Does quartzite need sealing, and can it take heat?
It depends on the slab. The Natural Stone Institute says granite and dense quartzites show naturally low absorption, and it also notes that some materials resist staining but still etch when acids reach them, and that sealing may be a deciding factor in choosing one. A dense quartzite that holds water on its surface may need little. A stone that darkens quickly in the water test is one we would talk about sealing before it goes in, and our general notes on that are in sealing and maintaining stone worktops.
Heat is the easier half. The same Natural Stone Institute paper says quartzite generally tolerates heat and changes in temperature well, which is the opposite of the advice for a resin-bound quartz top. If you have a slab picked out, or a name from a stone yard, ask us for an estimate and we will look at a sample of it before anything is cut.
Sources
- Geology.com, Quartzite — Quartzite forms when quartz-rich sandstone is altered by metamorphism; about seven on the Mohs scale; used for stair treads, floor tiles and countertops; some quartzite is sold as granite in the dimension stone trade.
- ASTM International, C616 Standard Specification for Quartz-Based Dimension Stone — Classifies quartz-based dimension stone by free silica content as sandstone (I), quartzitic sandstone (II) and quartzite (III); requirements for absorption, density, compressive strength, modulus of rupture and abrasion resistance.
- Natural Stone Institute, Comparative Performance of Natural Stone and Manufactured Slabs in Architectural Applications — Granite and dense quartzites have naturally low absorption; absorption varies by stone type and quarry; quartzite generally tolerates heat; some materials resist staining but etch with acids; sealing may be a deciding factor.
- Cambria, Product Care FAQ — Cambria quartz may not withstand direct heat from pots and pans; a closed-weave hot pad or solid trivet is recommended.
- Cambria, Planning and Care — Cambria quartz never requires sealing, polishing or reconditioning.
FAQ
Is It Really Quartzite? What to Check Before You Buy — questions
Is quartzite the same as quartz?
No. Quartzite is a natural rock formed when quartz-rich sandstone is changed by heat and pressure, and it is quarried and cut like granite. A quartz countertop is a slab manufactured in a plant and bound with resin. The names sound alike, but the two are made differently, behave differently under a hot pan and are cared for differently.
Is quartzite a natural stone or man-made?
Quartzite is natural. It comes from a quarry as solid rock, is cut into slabs and polished, and each slab varies with where in the quarry it came from. The man-made product people confuse it with is quartz, which is manufactured in a plant, bound with resin and sold under its maker’s own care rules, including no sealing at all.
How can I tell if a slab sold as quartzite is really quartzite?
Test a sample piece of that slab rather than going by its name, since stone trade names are commercial, not geological. We see whether the sample scratches glass, which a stone that is mostly quartz will do and a softer stone will not, and we put water on it to see whether it darkens.
Does quartzite need to be sealed?
It depends on the slab. Dense quartzite absorbs very little, but absorption varies with the stone and the quarry it came from, so one answer does not cover every slab with the name. We put water on a sample of yours; if it darkens quickly, sealing is worth discussing before the top is installed.
Is quartzite heat resistant?
Quartzite generally tolerates heat and changes in temperature well, according to the Natural Stone Institute, which is one of the reasons people choose it over quartz. Engineered quartz is different, and its makers recommend a trivet or hot pad under hot pans. A pad under a hot pan is still a good habit on any stone.