04 April 2010

Onyx isn't what you think it is

This post ran on 15 October 2008 originally.

The polished rock pictured above is true onyx. Onyx is a form of quartz called chalcedony (what a great word) that's usually associated with volcanic activity. As a form of quartz, chalcedony is composed of silica. It's formed when water dissolves silica to the point of saturation. What precipitates out of the saturated solution is chalcedony. Chalcedony, or true onyx, is a semi-precious stone that's used primarily to make jewelry.

The materials I'm showing above are sold as onyx, but they are an unrelated stone. Repeat, they aren't really onyx. That certainly doesn't distract from their beauty, but knowing what things are is important.

The stones shown above are a form of calcite called sinter. If you go to a stone yard and ask to see a slab of sinter they will look at you like you have three heads, so play along and call it onyx. Sometimes, knowing something and keeping it to yourself can be really satisfying.

Sinter, or commercial onyx is formed from calcite in a way similar to how travertine is formed. Water dissolves calcite from limestone to the point of saturation and what precipitates out of that solution will form either sinter or travertine depending on a couple of factors. If there are air bubbles present at the time that the calcite gets deposited then the resulting stone will be travertine. If there are no air bubbles, then the resulting stone will be sinter, or commercial onyx.

If you've ever been in a cave, the stalactites and stalagmites are made from calcite and if left to form large enough deposits, they may end up as a vanity counter several thousand years in the future.

What this means too is that this material is a sedimentary rock. Of the three types of rock (igneous, metamorphic and sedimentary), sedimentaries are almost always the most fragile and commercial onyx is no exception. It can't handle everyday stresses and it is very easy to chip and crack. People who don't know any better sell this stuff as real, silicaceous onyx. If it were silica-based, it would wear a lot better than this material actually does. Keep in mind that it is as high maintenance as travertine. I think travertine's gorgeous, it's my favorite flooring material. But I wouldn't put it on a counter if you put a gun to my head.

It can't handle heavy traffic or exposure to acids. It's extremely porous and makes a pretty lousy kitchen surface. Besides, most of it is supremely busy and a little of it goes a long way. In the bathroom pictured above, it looks interesting without being overwhelming. But just barely.

In the kitchen above it looks like the scene of a grisly murder or a slaughterhouse. Seriously, it looks like these people have a meat back splash. Ugh. This material is very expensive and as the kitchen above illustrates beautifully, expensive doesn't always mean tasteful.

The less garish form shown on the tub surround above is usually called honey onyx. I've used the same material as a desk top in an office and it looked interesting without being too too. Get up close and personal to a slab of the material pictured above some time if you get the chance. It's really interesting. It looks like half crystallized caramel. It's a little too wild for my tastes, but I can't walk past it without stopping. Sometimes, stuff that comes out of the ground is just jaw dropping.


  1. I used to sell stone countertops, so I am finding this all very interesting. First of all, I am still laughing at the trees/Baltic Brown tale from the last post. Next, I am so glad I didn't select travertine as my bathroom countertop after your comment. Third, that red backsplash/countertop combo. Wow. Wow.

    Happy Easter,

  2. Yeah, that meat back splash is really something. Sheesh! You needn't be a geologist to sell stone, but having an awareness of it is vital. I'm consistently amazed by people in the stone business who don't know what they're selling or even worse, don't have any interest in learning. It drives me crazy.

  3. You know.. I love bacon just as much as the next person.. but I wouldn't *decorate* with it..

  4. The countertop post series is AWESOME. I am seriously geeking out on the geology, and so excited that you have soapstone featured. I have soapstone tile countertops (I know what you're thinking...), but they're set edge to edge, epoxied, and sanded down, so that they look like a solid surface. Lovely, but oiling them is annoying. I actually loooove some of the onyx counters, but what I really want is marble. I'm pretty sure they'd end up a stained mess in no time, though.

    Now that I'm rambling, can I ask you a granite question? I kind of hate the granite, but what I really hate is the shine. I know black granite/gabbro can be successfully honed, but what about the creamy white granites? Some of them almost look like marble, but the shine is terrible (just my two cents).

    Ok, that was the longest, least cohesive comment ever. Sorry.

  5. Thanks Erin, that's means a lot. I get a real kick out of Design Crisis and your opinion means far more to me than it should. Hah!

    To answer your question, yes. Any granite can be honed. The granite people are aware of the rising backlash against shiny counters and they are coming out will all kinds of wild finishes for granite. I'm fond of a finish they're calling leather and another one they're calling brushed. Those specialty finishes transform even pedestrian granite into something all together new. Seriously. The first time I saw brushed uba tuba I had to be told what it was.

  6. Paul, you are too kind. Really! I appreciate your knowledge and informed advice -- it's harder than one might think to find on the interwebs.

    Anyway, my mom has a leatheryish marble (not granite) countertop. It's very pretty, but impractical from my point of view because the uneven surface looks hard to clean.

    We're thinking about moving soon, so I spy a kitchen remodel in the near future. This time, I want something indestructible (but pretty, of course). Would a honed white granite show stains, rings, surface blemishes, etc?

    Also, I'm curious as to what you have/would choose in your own kitchen...

  7. Oh believe me, I know how hard it is to find accurate information on the web. In fact, I feel singularly responsible for the defense of white marble as a kitchen surface. Contrary to what the solid surface and quartz people (the granite people too) will tell you, marble is not a horror show.

    A couple of years ago some friends and I rented a villa in Sorrento. It was my distinct pleasure to cook on its 150-year-old Carrera counters and they were glorious. They were patina-d and worn and I swear I fell in love with them. My passion bordered on the erotic.

    Marble isn't a piece of plastic and it does show wear and tear. I think that's one of its positive attributes.

    It is not for everybody though. For me though, when I re-do my place, it's going to be an homage to Carrera.

    If you have kids and you're worried about the wear patterns I love that's fine, there are a number of quartz products that look surprisingly like the real thing. Caesarstone even comes in honed finishes now.

    So check out Caesarstone and if you'd rather a natural stone, it's hard to beat soapstone in the wear and tear department. My only request is that you don't get Corian. Hah!

  8. Now, don't you go putting expensive ideas into my head, Paul... Carrera is the mostest, for sure. Perhaps I could sell my firstborn, solving both the financial and wear/tear issues in one fell swoop? ;)

    Ok, done pumping you for info. For now. But, like the Terminator, I'll be back.

  9. Believe it or not, Carrera's one of the less expensive marbles out there and it costs less than a lot of granites and quartz products.

    Pump me any time sister. I'm adding you to my blog roll.

  10. Thanks, dude, I added you to ours.

    And I know that Karly is redoing her kitchen this year, so I guess I should have said that WE'll be back ;)

  11. What do you think about carrera marble counters in a bathroom with children? The stone store we went to was very down on the idea and really pushed granite, but we don't care for granite and prefer the classic marble, but we don't want to make a mistake either.


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