Is it granite, gabbro or basalt?

This post ran on 17 October 2008 originally
--------------------------------------------

This is Absolute Black. It is always labeled and sold as granite but it isn't granite. It's a mineral called gabbro.

When magma gets trapped in a single layer underneath the earth's crust, it will gradually cool and form gabbro. Now if the same material were to be pushed up from below under great pressure, it would form granite. But then again, if that magma were to come in contact with water it would turn instantly into basalt. Are you still following me here? Gabbro, granite and basalt are essentially the same material in different forms. In order to form granite, magma needs a good hard squeeze so its component materials can separate and form large crystals. If magma cools very quickly upon contact with air or water, it will form basalt. And if magma is left alone for a couple million years it will form gabbro.

Why is this important? Well, it's important because those three phases of former magma have different properties. Basalt is the most brittle of the three which is why it doesn't get used as counter top material. Most granites are strong enough to be sliced into 3cm sheets without too much trouble. But gabbro, due to its uniform crystal size and density is stronger than granite. This means that it can handle longer, unsupported overhangs --like on a bar. It can be carved into more ornate edge treatments and since it's so uniform, it is more water resistant. Absolute black is a great stone to make into a sink, whereas you wouldn't want to use most granites for that purpose.

The downside to it (if it's truly a downside) is that it's always black or very nearly black. Chances are good that if you're looking at a uniformly black or very dark grey granite, you're not looking at a piece of granite at all, but rather a piece of gabbro.

Now, due to that uniform crystal size and density, gabbro can be shined up to a mirror-like surface and that's where the problem with it is as it's ordinarily used comes in. It is impossible to keep clean if it's being used as a kitchen counter when it has that mirror finish. I have never heard of someone who had it and liked it. But the problem isn't the material, it's the finish. It will show every finger print, water spot, smear and smudge. It would drive me insane.

Here's a slab of absolute black with a honed finish. The honed finish tones down the black quite a bit, and in so doing, it eliminates the mirror effect.

Here's a whole kitchen done in honed Absolute Black. It's a much calmer counter than the shot at the top of this post, wouldn't you say?

Now, because true Absolute Black "Granite" is a premium, a lot of less-than-honorable stone suppliers will take a less-expensive predominantly black granite and call it Absolute Black because most people can't tell the difference.

Sometimes; similar, dishonorable suppliers will actually dye inexpensive granite with black pigments and sell it as more expensive Absolute Black.

Not that I'd know any of these less-than-honorable business people personally...

Anyhow, if you're in the market for absolute black, make sure that what you're buying is just that. If it looks like this, it ain't absolute black.

And as a completely unrelated yet completely cool side note, the paving stones on the streets of Pompeii are gabbro.

Sometimes I just love geology. Even if the only person I fascinate with this stuff is me.

Working up a lather with soapstone

This post ran on 16 October 2008 originally.
--------------------------------------------

Another metamorphic rock that makes its way into homes is steatite, commonly called soapstone. It's composed primarily of the mineral talc with a healthy does of magnesium for good measure. The magnesium is where it gets its grey color. Soapstone formation occurs in regions of tectonic subduction and in the presence of water. Let me whip out my rock phase illustration again.

By the time a slab of soapstone ends up in some one's home, it's between 400 and 500 million years old to give you some sense of the timeline involved in its formation.

Soapstone is soft. You can write your name in it with a fingernail is how soft. Due to its high talc content, it feels somewhat like a bar of soap to the touch, hence its name.

Even though it's very soft, it's an excellent material for kitchen and bath counters. Unlike a lot of stone, soapstone is neither alkaline nor acidic and is completely inert. That means that virtually nothing can make it react chemically. Vinegar and lemon juice, the great etchers of marble, have no effect on soapstone. It's virtually non-porous, so oils and dark-colored liquids can't stain it.

The stuff's used for table tops in chem labs for a reason.

Most people oil their soapstone with mineral oil but this doesn't do anything but enhance its color and minimize the appearance of the hairline scratches it will accumulate over time. In its un-oiled state, soapstone is grey. Add mineral oil and it turns black. With repeated applications, this oil-induced black color will become permanent, but that's due to the oil oxidizing on the surface of the stone.

Soapstone's an excellent heat diffuser and that's why it gets used to make fireboxes and wood stoves. It's also water proof and that's why it gets used to make sinks and cookware.

Soapstone is a great material to use in a kitchen. Its grey-black color is an achromatic neutral and that means it will go with anything. If you're considering a kitchen renovation and you want to try something different but still a natural stone, think about soapstone.

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.

Let's meet marble and the metamorphics

This post ran on 14 October 2008 originally.
---------------------------------------------

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 cadmium, chromium and the rest of them are trace amounts; but I'd like to keep my cadmium 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.

Here's a working definition of granite

This post ran originally on 13 October 2008

--------------------------------------------

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.