Stone GuidesIs This Normal?

Is It a Crack or a Fissure? Lines in Granite Explained

A thin line in granite is often a fissure, a natural part of the stone and not a defect. How to tell it from a crack, what causes real cracks, and when to call.

4 min read

You run your hand across the counter and see a thin line in the stone. Before you worry, know this: many lines in granite are part of the stone itself, and they were there when it came out of the ground.

The facts below come from the Natural Stone Institute, the trade group for the natural stone industry, and Use Natural Stone, its website for homeowners.

Fissure or Crack: The Difference

Use Natural Stone puts it simply: “A naturally occurring break in a stone slab is called a fissure.” If the break is human caused, “(during fabrication or handling, for example), then it’s considered a crack.”

Fissures are normal. The same article says “Fissures in stone are a perfectly normal occurrence. All kinds of geologic stresses can cause a stone to fracture, and in many cases, these areas heal themselves with minerals carried along by groundwater.”

So a fissure is not a flaw in the work. It is part of the stone’s history.

The Fingernail Test

Use Natural Stone gives one easy check: “Can you feel the edge of a fracture on the slab’s surface? If not, then the cracks/fissure is unlikely to be a problem.”

Run a fingernail across the line. If it glides over smoothly, that is a good sign. If your nail catches on an edge, call us and we will tell you what we see.

Pits and Small Marks

Small pits are part of natural stone too. Use Natural Stone notes that you may want some parts of a slab in a less visible spot “because of natural pits or fissures.”

Many slabs are treated at the factory to fill them. The Natural Stone Institute says “many species of granite receive a resin treatment at the factory,” and that it “is used to fill micro-fissures, indentations and other minor characteristics.” It calls these marks “birth marks,” not defects.

What Causes a Real Crack

Granite is strong once it is installed. Use Natural Stone says “Weaknesses in the stone are mostly a concern during fabrication, transportation, and installation. Once the stone is in place, it’s not likely to break as long as it’s well supported underneath.”

Two things change that.

Sudden heat. The Natural Stone Institute says direct, local heat is discouraged, “since strong thermal gradients within the stone can initiate cracking.” Use a trivet under hot pans. Our hot pans guide explains why.

Poor support. Stone needs a solid, level base. Our checklist for template day says it plainly: cabinets need to be strong enough to hold stone, and poorly braced cabinets can let it crack. Raised bars and big overhangs need supports too.

Can a Crack Be Fixed?

Often, yes. Use Natural Stone says “Granite countertops should be repaired by a professional,” and “Most of the time, a color matched epoxy can be used to fill the void and it will be virtually invisible.”

It also says this is uncommon: “It is rare to get a crack or chip in your countertops.”

If you are not sure whether a line is a fissure or a crack, call us and describe it.