What Scratches Stone, and Why

The Material Science Behind Surface Preservation

Most cleaning professionals learn what products to use. Far fewer learn the material relationships that determine whether a surface remains intact over time. The Mohs hardness scale provides one of the clearest frameworks for understanding how surfaces respond to contact, and it explains why one material stays unmarked while another shows premature wear.

Once hardness is understood, tool selection becomes intentional rather than reactive. Scratching becomes predictable rather than surprising. Surfaces behave consistently because the physics guiding each interaction are known in advance.

The difference between an $800 countertop restoration and a $6,000 replacement often comes down to a single number on this scale. A number that describes how one material interacts with another at the most fundamental level.

The Principle That Governs Every Interaction

In 1812, German geologist Friedrich Mohs needed a field method for identifying minerals. He ranked them by which one’s scratch which. Diamond scratches everything. Talc gets scratched by everything. The scale runs from 1 (talc) to 10 (diamond), and every material falls somewhere on this spectrum.

The principle is absolute: a material with a higher Mohs number will always scratch a material with a lower number. Always. Regardless of pressure, angle, or how careful you believe you're being. A Mohs 7 material dragged across a Mohs 4 surface will leave scratches. This is not a tendency or a risk factor. It is physics.

What the scale does NOT measure matters equally. Hardness is not durability, not density, not heat resistance, not chemical reactivity. Glass registers around Mohs 5.5, harder than most natural stones, yet it shatters on impact. Marble registers 3 to 4, soft enough to scratch with a copper penny, yet marble buildings have stood for millennia. These are different properties entirely. Confusing them leads to flawed assumptions about what materials can and cannot withstand.

Will a Magic Eraser Scratch My Marble? (Yes, and Here's the Physics)

Melamine foam, sold under brand names like Magic Eraser, registers at Mohs 4. Marble registers at Mohs 3 to 4. When you drag a Mohs 4 material across a Mohs 3 to 4 surface, you remove material. Every pass. Without exception.

This is worth understanding precisely because melamine foam feels soft. It compresses. It seems gentle. But hardness and softness to the touch are not the same as hardness on the Mohs scale. Melamine foam works through abrasion, not chemistry. It is, in effect, very fine sandpaper in foam form. On glass (Mohs 5.5) or porcelain (Mohs 7), this makes it remarkably effective. On marble, travertine, or limestone, it micro-sands the surface with every use.

Industry guidance advises against using melamine foam on natural stone. This isn't excessive caution. It's material science. If the surface you're cleaning is Mohs 4 or below, melamine foam will damage it, regardless of how lightly you press or how briefly you work.

What Floor Pad Colors Actually Indicate

The color coding system for floor pads exists to communicate aggressiveness, not hardness. White pads are the least aggressive, designed for polishing and light buffing, typically containing minimal or no abrasive particles. Red pads step up for spray buffing and light cleaning. Blue and green handle scrubbing, with green more aggressive. Brown and black are stripping pads, engineered to remove floor finishes entirely.

Stone restoration professionals use white pads on marble regularly. The pad itself, when clean and used for its intended purpose, is appropriate for soft stone. The failures happen when pads are used outside their designed application, or when they've accumulated debris from previous jobs.

This is the detail that matters: a clean white polishing pad is safe for marble. A white pad that picked up grit from a concrete floor last week is now a carrier for particles harder than marble. It will scratch anything softer than that trapped grit. This is why restoration professionals inspect pads before every use, why pad hygiene protocols exist, and why a pad that looks clean may not be clean enough for soft stone.

The same principle applies to microfiber cloths. When kept genuinely clean, microfiber is appropriate for routine stone care. But microfiber is effective precisely because its structure traps particles. If those particles include anything harder than your surface, you've converted a cleaning tool into an abrasive one.

Quartz vs. Quartzite: Why the Confusion Costs Money

These two materials are mislabeled constantly, even by installers and fabricators who should know the difference. The names sound nearly identical. The appearance can be similar. The care protocols are not.

Quartzite is a natural metamorphic rock formed when sandstone undergoes extreme heat and pressure. It registers between Mohs 7 and 8, harder than granite. It tolerates aggressive mechanical cleaning. It's chemically inert, meaning acids that would destroy marble won't affect it. It requires sealing to prevent staining.

Engineered quartz (Silestone, Caesarstone, Cambria) is a manufactured composite: roughly 90 to 94 percent ground quartz crystals bound with polymer resins. The finished product registers around Mohs 7, comparable to the natural quartz mineral it contains. But the resin component introduces vulnerabilities that natural quartzite doesn't have. Engineered quartz is heat-sensitive. Certain chemicals that wouldn't affect natural stone will damage the resin matrix. It never needs sealing because the resin already makes it non-porous.

The field test: try to scratch a piece of glass with the stone. Natural quartzite, at Mohs 7, will scratch glass easily. If the stone won't scratch glass, it's likely mislabeled marble or dolomite, regardless of what the invoice says. This takes thirty seconds and prevents protocol errors that void warranties.

The Assessment That Should Precede Every Protocol

Before any tool or product touches a surface, professionals who understand material science ask five questions. The answers determine everything that follows.

What's the finish?

A polished marble surface behaves differently than a honed one. Polished finishes show scratches more readily because the mirror surface creates contrast. Honed finishes hide minor abrasion but stain more easily because pores remain open. Leathered finishes trap debris in their texture, debris that becomes abrasive during cleaning if not removed first.

Where was it sourced?

Marble from Carrara, Italy behaves differently than marble from Vermont or Turkey. Mineral composition varies by quarry, affecting both hardness and chemical reactivity. A care protocol developed for one variety may damage another.

What's the sealer situation?

Impregnating sealers penetrate the stone and protect against staining without changing surface hardness. Topical sealers sit on the surface and create a sacrificial layer with its own hardness properties. You may be cleaning the sealer, not the stone, and the sealer may be softer than the stone beneath it.

What's been applied previously?

Previous cleaning products, polishes, waxes, and enhancers leave residues that interact with new products. A surface that appears to be natural stone may be buried under layers of product buildup. Sometimes the only path forward is stripping to bare stone and starting over.

Natural or engineered?

As covered above, this single distinction changes heat tolerance, chemical sensitivity, sealing requirements, and long-term maintenance protocols entirely.

Surface Hardness at a Glance

Mohs	Materials	Tool Implications
2-3	Gypsum, talc, soft limestone	Soft cotton only, no mechanical pressure
3-4	Marble, travertine, limestone, copper	Clean microfiber, white pads only, no melamine
4	Melamine foam	Will scratch anything at or below this level
5-6	Glass, ceramic tile	Standard tools appropriate, melamine safe
6-7	Granite, porcelain	Tolerates more aggressive cleaning
7-8	Engineered quartz, natural quartzite	Highly scratch-resistant (chemical sensitivities vary)

Why Mechanical Damage Matters As Much As Chemical Damage

The cleaning industry invests heavily in chemistry: pH levels, surfactant concentrations, enzyme formulations, dilution ratios. This expertise is real and necessary. Using the wrong chemical on the wrong surface causes damage that ranges from cosmetic to catastrophic.

But mechanical damage gets a fraction of the attention, and it shouldn't. Scratches from abrasive tools, micro-abrasions from improper pads, surface haze from cleaning implements harder than the material they're touching. These problems accumulate quietly. By the time they're visible, the damage is done.

Chemical and mechanical damage require different knowledge. One asks: what's the pH, what's the composition, what's the reaction? The other asks: what's the hardness, what's making contact, which material wins?

Building This Into Practice

Start with an audit. Examine every pad, cloth, and compound in your inventory against the surfaces you're responsible for maintaining. Research Mohs ratings for both. Identify mismatches.

Build surface-specific protocols that specify tools, not just products. Document the reasoning. Make the physics explicit. When new team members join, train them on why before you train them on what. People who understand principles follow procedures more consistently than people who've memorized steps without context.

The Mohs scale is over 200 years old. Physics haven't changed. But the application of this knowledge to surface care is only now reaching the cleaning industry. Restoration professionals have operated with this framework for decades.

Now you can, too.

We don't guess. We assess. And it starts with understanding what happens when two materials meet.

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