Frederick M. Hueston, PhD

It was another brisk, cold day here in Florida. Yes, it does sometimes get cold in the Sunshine State. Of course, cold for us is any temperature below 52 degrees. I like to call this the weather we don’t tell the tourists about! So, I prepared to face the bracing cold, grabbed my trench coat, fedora and boots and headed out the door on my way to my local greasy spoon for a hot cup of joe and some ham and eggs.  Just as I got into the old Woody my cell phone rang. I hauled it out of my coat pocket and flipped my phone open. Yup, this old man still has a flip phone.

“Stone Detective, here,” I said in a voice that I’m sure sounded like I wasn’t awake yet.  

“Hey there, it’s Robert, from Fabricators.” Robert happened to be an old friend of mine. 

“What’s up, Robert?” He said he had a problem that really confused him, and he couldn’t think of anyone else to call but me. He went on to explain that he had a granite countertop they had recently installed, and the customer complained that it was developing some pink spots. He said he went out to check on the top and there were no spots. The customer swore that these spots were there yesterday! I told him that he should tell the customer to have his eyes checked (LOL). We both laughed and then he said that he got a call the next day from the same customer, and the spots were back. This time when he ran out to check, sure enough – the spots were there. I asked him if he could send me a pic. He said he did take a few, and would email them to me right away. I went for breakfast, pondering what this problem might be. Maybe some hot joe would kick my brain into gear.

No, the pink coloration in the granite is not due to some odd reaction to resin, glues or some impregnating sealer. Take another guess…

No, the pink coloration in the granite is not due to some odd reaction to resin, glues or some impregnating sealer.  Take another guess…

I walked into the diner and bless her, Flo had already poured me a cup of joe. I greeted her with a nod as well as some of the regulars that I see practically every morning. “Ham and eggs, again?” Flo asked me. I grunted and nodded “yes” as my phone alerted me that I had an email. Well, this darn flip phone doesn’t let me read my emails, so I ran out to the woody to grab my tablet. Yes, I do have a few modern devices as well. 

I hurried back into the warm diner, just as Flo was sliding my plate onto the counter. I should have stopped to eat, but I had to see what these pink spots were all about. 

I opened my email and found some close-up pics of a Delicatus granite with numerous pink spots throughout the countertop. The spots looked like some pink Kool-Aid had been spilled on it.  Normally, I would recommend a poultice, but it puzzled me that the spots would disappear and reappear. 

My first suspicion about the culprit was something bleeding from underneath the top. If that was the case, this might be one mystery that I would be unable to solve. I called Robert back and asked if he could send me a section of that granite type, so I could not only observe these spots in person, but also send it out for analysis.

I closed my tablet and started to attack my breakfast, but I sensed a kind of chill not associated with the weather. I ain’t as dumb as I look. I apologized to a frowning Flo before chowing down.

Several days went by and the stone finally arrived. I opened the box and there was a 12-inch by 12-inch sample of Delicatus granite. The problem was there were no pink spots. I got on the phone and called Robert to ask him why he didn’t send me a spotted sample.

Well, long story short: He said it had several pink spots when he packaged it up. Well, either he needed his eyes checked or I needed new glasses.  

I decided to follow a hunch and expose the sample to some sunlight, and placed the sample outside my office. Viola! The next day the spots were back. Now I was really perplexed, so it was time to send it off to the lab for testing.

Testing took about three weeks but when I got the results, I had my answer. This type of granite has a mineral known as Hackmanite, and Hackmanite has what is known as Tenebrescence. The following is what this term is and why the granite has pink spots that disappear.

Tenebrescence is defined by minerals that are able to make a color transformation; minerals that display the ability to change color in this fashion are termed tenebrescent. Tenebrescence is the property that some minerals and phosphors show of darkening in response to radiation of one wavelength and then reversibly bleaching on exposure to a different wavelength. Very few minerals exhibit this phenomenon, also known as reversible photochromism, a term that also is applied to sunglasses which change color density on exposure to sunlight.

Hackmanite will change color from pink to gray or another light color. As the light changes in someone’s home, the countertop may be exposed to different UV wavelengths.  Another mystery solved. Best of all, Robert was able to spin the explanation so his clients understand they have a rare and interesting stone that makes their countertops unique.

The Stone Detective is a fictional character created by Dr. Frederick M. Hueston, PhD, written to entertain and educate. Dr. Fred has written over 33 books on stone and tile installations, fabrication and restoration and also serves as an expert for many legal cases across the world. Send your email comments to him at