Dear Slippery Rock…

The Slippery Rock regularly receives email from readers commenting on articles, or asking our opinion on stone-related problems, but seldom do we hear from homeowners outside the industry.

This recent letter presented a learning experience for both us and the homeowner who posted the problem. We reached out to two of our writers familiar with geologic puzzles, and fabrication mysteries.  – The Editor

Good afternoon. 

Sorry to be another homeowner begging for your expertise concerning cracks, fissures, and veins.  Would you mind providing your opinion of the attached pictures?  As you can guess, the fabricator says the dark cross-grain vertical line in the marble where the faucet would mount & backsplash is natural, and was not a repaired piece of marble.  I disagreed and had them take it back.  They are not providing any solution to the problem and not backing down so I thought I would get your opinion.  Any info you can offer is greatly appreciated.  Thanks.

Crack repair or natural fissure?

Crack repair or natural fissure?

Crack repair or natural fissure?


Dear Joe,

First, this is a beautiful piece of stone with a lot of character. The area you are concerned about is a prime spot for a break to occur, so your concern is understandable. I can see why a fabricator might want to preserve it, if it were to break in half. Zooming in on your photo, it appears to be natural –the white vein in the center appears to be crystalline – not easily faked. 

In reality, this is probably Mother Nature making the repair –  and not the fabricator. This could be an example of a pretty complex piece of geologic history, showing the bed plane and a relief fissure – the dark band which looks like a crack or repair, to you. 

With your permission, I am going to consult a couple of specialists; one is a geologist who writes for us and the Natural Stone Institute, and one serves as an expert witness in litigation involving stone failures, and installation failures. I’ll send their replies and opinions on this issue. 


From: Karin Kirk: 

Dear Slippery Rock,

I  love geological puzzles like this!

First off, this is not marble, it’s limestone. You can tell because of the fossils and “pellet” shapes in the stone — all of those features are erased when limestone metamorphoses into marble.

Secondly, the stone is an interesting one because of the bands of very fined-grained, crystalline material that run through it. Those parts look like onyx and most likely formed in a similar way. Dissolved calcite was circulating with groundwater and filled in the cracks in the stone. This process of natural mineral ‘glue’ is common, and in fact that’s how sedimentary rocks get stuck together to form solid rocks.

Lastly, yes, it’s common to have a set of fractures or “joints,” as geologists call them, that run perpendicular to the bedding planes. It’s the stone’s way of decompressing and offloading stress. Most rocks form deep underground and when they get uplifted and find themselves on the surface of the Earth, they develop fractures because they are no longer being squeezed so tightly.

The fracture looks natural to me — it looks like a joint filled with calcite, which is especially recognizable from the subtle lines and milky white color within the mineral deposit.

Hopefully they can transport the piece and get it installed - and/or if it does break, perhaps it’s repairable since the fracture is already there and it won’t look much different if they ended up needing to repair it along that plane. … Sometimes the filled joints are stronger than the rest of the rock, but sometimes not.

Often customers are okay with something once they are assured they are not having the wool pulled over their eyes. Offering a credible explanation for why the feature is in the stone seems to help people come around to it. Once they know the ’story’ they often tend to like it!

–Best Regards,

Karin Kirk


Fred Hueston

Stone Forensics

Hello Slippery Rock,

What I can tell from the pic – lucky it’s a higher resolution photo – it does look like a natural vein. One way to tell would be to run your fingernail across it. If your finger nail catches, it may be a crack. If it doesn’t catch then it may be a natural fissure. 

Another method we use is to take a blue light and examine it. If it was a crack and it was filled with a resin, it will show up under the light.

Hope this helps!



We forwarded these two expert opinions on to the homeowner.

We hope he’ll accept our advice, but it will be up to him to apologize to the fabricator and accept this stone with a interesting geologic story. It certainly is in the best interests of both parties. 

Fabricators: here’s a case where a little knowledge of geology could help you out of a dispute. Learn as much as possible about the different features of stone you sell and install, and educate your clients.