Onyx is not what you think

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.

The Bailout explained

Paddy Hirsch, senior editor of NPR's Marketplace, released another video that explains the bailout in easy to follow terms. He explains what's happening in the financial markets, what the Fed and the Treasury's plan is to fix it and what's at stake. Brilliant!

The credit crisis as Antarctic expedition from Marketplace on Vimeo.

Marble and the metamorphics

That sounds like the name of a Do-Wop band. So since I touched on igneous rocks in general and granite in particular yesterday, today I want to talk about the metamorphics.

My diagram above shows sedimentary rocks on a sea floor being subducted under a tectonic plate. That sedimentary rock will turn into metamorphic rock given enough time, enough heat and enough pressure. So what was once sediment on the bottom of the sea turns into metamorphic rock as it gets pushed down into the slow cooker that sits directly below our feet. If it doesn't run into anything, it will turn into an igneous rock eventually. But then I wouldn't have anything to write about.

So in our case, the now metamorphic rock is going to run into another continental plate and instead of continuing its long journey down, it's going to be thrust upward like in this diagram.

The blue section in this diagram shows how metamorphic rocks end up back on the surface of the earth after their time spent below ground. That blue section is how we get three common metamorphic rocks used in homes: marble, quartzite, soapstone and a fourth, mysterious stone called serpentinite. I'm going to write a post on soapstone later, so for now I'm going to concentrate on marble, quartzite and serpentinite.

Everybody knows what marble is but what a lot of people don't know is that it used to be limestone, a sedimentary rock. So even though the chemistry of the original limestone and the resulting marble are identical, their molecular structures are different thanks to time spent in the depths of the earth. The same thing happens to turn sandstone into quartzite. Serpentinite is another metamorphic rock that's usually mislabeled as marble (Rainforest Green and Rainforest Brown are examples of serpentinite). Serpentinite starts out as ultramafic rock in the mantle of the earth that gets thrust upward. Serpentinite never spent any time at the surface of the earth and it isn't a transformed sedimentary rock. It's instead the transformed, formerly molten core of the earth.

OK, real life example time.

Here's a slab of Carrera marble. It's a pretty common stone so far as marbles go and most of it starts at around $60 a square foot when it's being made into a kitchen counter. It's composed of calcium carbonate and other minerals and that's what makes it softer and less stain resistant than granite. Despite what everyone claims are its negatives, I'd be safe in saying that it's my favorite counter top material. It's a classic, it holds a temperature perfectly, it looks great and 11 million Italian families can't be wrong. Embrace the stains people.

So here it is in a traditional kitchen. The subway tile on the back wall is also made from Carrera in this kitchen. In life, this is a gorgeous kitchen in a nearly timeless style.

Carrera also looks great in a modern setting. The William Ohs kitchen shown above proves that pretty well.

Marble can also be black with white veins of silica in it and that's stunning in its own right. Although at the end of the day, I think that white marble's easier to work with aesthetically.

This is a piece of white quartzite my client fell in love with last week. White quartzite often gets mislabeled as marble, but they are very different stones. Marble is composed of calcium carbonate and quartzite is composed of silica. The two stones behave very differently. As silica, quartzite will be harder and less prone to staining than marble will. If you look at quartzite up closely, you can see that it has a grainier appearance than marble does. That's from its once having been sandstone.

Quartzite usually has some bright colors in it on a white background. When it looks like this it's often mislabeled as granite and that's unfortunate because it's not granite. Quartzite is more porous than granite is despite their being made from the same elements essentially.

This is a quartzite from Brazil that's always mislabeled and sold as a granite. It's usually called Blue Louise and it is an eyeful. Again, it's beautiful as a piece of stone but as Tim Gunn would say, it's a lot of look. Proceed with caution.

The other big difference between quartzite, marble, serpentinite and granite is the price. Quartzite and serpentinite are always wickedly expensive whether they're labeled properly or not. Marble and granite tend to be more affordable.

Finally, the slab of stone above is always labeled as a marble and it's usually called Rainforest Brown or Rainforest Green. It's not a marble though, it's a serpentinite that's been pushed up from the very bowels of the earth. It's made from a veritable soup of elements ranging from manganese, cobalt, nickel, iron and silica. Even though it's sold as a marble, it's a lot more resilient than marble is and it's usually harder. These stones are great to use in bathrooms, but I wouldn't want to prepare food on them in a kitchen owing to their toxic mineral content.

Granted, the amounts of cobalt, chromium and the rest of them are trace amounts; but I'd like to keep my cobalt intake down to zero thank you.

So there's my run through of some common metamorphic rocks. Tune in tomorrow when I tackle the sedimentary rocks people welcome into their homes.

A working definition of granite

The term granite, as it's used commercially, is a bit of a generic term. Now I'm not a geologist but I do have an understanding of the fundamental geology that goes into the dimensional stone that ends up in peoples' homes.

Granite's generally accepted to be an igneous rock composed primarily of silica that's formed in the mantle of the earth as magma gets squeezed between cracks in the earth's crust. As a liquid at that point, the magma tries to rise to the surface. It cools very slowly and under very high pressure then forms what are called batholiths --essentially huge domes that lie below the surface of the earth. These large formations are exposed later through the actions of erosion and thrust faulting. Due to the high pressure under which the magma cooled, the component minerals in it (quartz, feldspar, aluminum oxide, iron oxide, etc.) can crystallize. That crystallization is what makes granite granite.

I bring that up because of this granite right here, commonly called Baltic Brown.

You can see from this close up that Baltic Brown has circular crystals in it. They are in varying sizes but most of them are about two inches in diameter. Those round crystals are made from potassium feldspar and they formed about a gazillion years ago as some magma cooled underneath what is now Finland.

About eight years ago I got into it with a salesperson at a granite wholesaler who claimed that those round shapes were the remains of a stand of young trees that were run over by a lava flow and got fossilized in the process. People who don't understand what they're selling are a pet peeve. Claiming to have fossils in a slab of granite goes beyond not knowing and crosses the line into the idiotic. I don't expect granite salespeople to be able to rattle off the names of the component minerals that make up what they're selling, but some basic knowledge is most definitely in order.

Granite that ends up as counters gets cut into slabs and polished. From the cut stone, you get a really nice cross section of the crystal structure of a particular granite. Those crystals are where granite gets its sparkle and depth. A granite that was left to its own devices as it cooled and formed over the millennia will have a pretty regular pattern and color.

But when granite's actually moving as it cools, or if it runs into water, all sorts of things happen to it. A lot of times granite will run into other kinds of rock as it moves, so it will have incursions of schist and skarn and a host of other materials in it. A lot of times water will make iron oxide gravitate into cracks in the rock. Every component mineral in a granite has its own characteristics and reactions and that non-uniformity is at the root of granite's appeal. The slab below has incursions as well as lines of iron oxide in it.

It's an interesting stone as a stone, but it's a lot to try to pull off in a kitchen counter. I mean, it's pretty loud. Something like that I'd like to hang on a wall to admire. It tells a really compelling story but it's not something I'd want to see in one of my kitchen projects.

Patterns like that granite above are still pretty popular though that popularity has crested and is starting to wane. People are starting to look for other materials to use as counters and that's what I'll be writing about all week. Woo-hoo!

But in the meantime, if you like granite then get granite. Don't believe the stories of its propensity to stain or crack or even be radioactive. Almost every negative you hear about granite is chatter generated by a competitive marketplace. I have never actually seen someone stain or crack a granite counter. Nor have I ever heard of someone who had to reseal their counters. The radon hype is yet another non-story generated by the solid surface people to prop up their decidedly inferior products. Granite is harder than just about anything it will come in contact with and it will continue to look as good as it did the day it went in for the rest of the time you have it.

But let's look at some options anyhow. Tomorrow's going to be marble and the metamorphics.

The rocks in my head, an introduction

Rocks are divided into three categories: sedimentary, metamorphic and igneous. A lot of times these three classes are referred to as phases because each class can morph into each of the other classes over long periods of time. But that's can morph, it isn't automatic.

In English, those three classes can be pretty broadly defined like this: sedimentary rocks are formed by compacted sediment, metamorphic rocks are rocks that are transformed by heat and pressure after they're already formed and igneous rocks are formed by cooling magma. Some examples of sedimentary rocks are limestone and travertine. Some metamorphic rocks are marble, quartzite, soapstone and slate. Finally an igneous rock that's in a lot of peoples' homes is granite.

In the chart above, there's a delineation made between intrusive and extrusive igneous rock. Intrusive means that a formation of igneous rock rises into the earth's crust but doesn't break the surface. Not breaking the surface results in a very particular crystal structure. Extrusive igneous rock breaks the surface and cools quickly when not under pressure. This results in a different structure even if the magma has the same composition.

So there's my breakdown of the three classes of rock. There are examples of all three classes that end up being pressed into use by humanity and I'll be spending some time explaining them further. First up will be granite.