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Getting to Know Your Stone by Testing

It can be a real challenge understanding what material you are selecting for your home. In the stone world there are a range of terms that can make the identification of a surface material challenging. Labeling and naming conventions are only one area that cause confusion. Even after a person is familiar with the differences between stone materials, it can be a challenge actually knowing exactly how a given slab will actually perform. In this article we are going to take a look at how testing can help you to, not identify a stone, but verify its properties. Knowing the properties of a stone is what helps one make a correct identification.

Considering Which Tests to Perform

Testing natural stone surfaces to get actual data to identify a stone is very effective. But what test should you perform? Well, here we are going to look at three basic ones. These are not complicated tests. Each one allows you to determine a specific property of the stone in question.

Is the Stone Calcareous?

One of the first things to test is the nature of the mineral content in the stone. We are not saying that you need to figure every mineral that the stone contains. Rather, we are simply saying that it is good to get an idea of whether the stone is calcareous or siliceous. So what do you do to find out if a stone slab is calcareous? How does the test work?

The way to find out if a stone is calcareous is to do an acid test on the stone. An acid test reveals the presence of calcium carbonate - the main mineral in calcareous stone. If a large part of the stone is made up of calcium carbonate, then the slab is calcareous. If not, then the stone is most likely either siliceous or a man made surface.

The test works like this: using an acidic liquid, pour a small amount of the liquid on the stone. It is important to do the test in multiple locations and in areas that will not be visible. Testing on the backside of a stone fulfills this requirement. If the stone begins to fizz, the stone is calcareous. If nothing visibly happens, the stone is not calcareous. Why does this test indicate calcareous stone? Because calcium carbonate reacts with acids. In fact, it is an antacid. So when acid and calcium carbonate meet, they react and the reaction produces the fizz and it destroys the calcium carbonate and the acid. In other words, they neutralize each other.

If the stone is calcareous, then it is most likely (or should be) labeled as one of the following:

  • Marble
  • Banded Calcite (Commercially Called Onyx)
  • Limestone
  • Travertine
  • Alabaster

Knowing the type of rock the slab is made of indicates what degree of care and maintenance you will need to perform to keep it looking new. Granted, some people prefer the patina of calcareous surfaces. But it is good for you know going in which type of rock your surface is.

So that is the first test you need to do when getting to know your stone by testing. Next up, the porosity.

What is Its Absorbency?

To find out the absorbency of a slab, you can use an absorbency test. Like the first test we mentioned, this test needs to be done in several areas of the stone. Why is an absorbency test important? The short answer is similar to the one mentioned in the previous section of this article; care and maintenance.

This test, unlike the acid test mentioned previously, is non-destructive and it will be one that you can perform repeatedly over time. Let's look at what the test tells you and how you do it.

The absorbency test tells you how "thirsty" a stone is. In other words, how fast is the stone taking in liquid? Now at first, the porosity of a stone is what determines this. The more porous, that faster it will absorb water. However, stone slabs can be treated with sealer for natural stone to inhibit the absorption. These sealers come in many forms. For a countertop in a kitchen it may be good to select a food safe kitchen countertop sealer. The idea here is that periodically applying a sealer to the stone makes it less absorbent. And the denser the stone is at the beginning, the less sealer you will need to use.

The absorbency test is done like so: simply pour some water on the slab at various locations. Observe the rate at which the water is absorbed into the stone. Periodically, this test should be performed in order to determine whether it is time for another sealer application. Additionally, it is important to clean a sealed stone using a pH neutral cleaner. Cleaners that are not formulated properly will destroy the sealer that is inhibiting the absorption.

How Hard is the Stone?

The last of the three stone tests that we are going to talk about here is the test you perform to check the hardness of the stone. This is called a scratch test. Like the first two, this third test is also simple to perform and the only thing you need in order to do the test is a material of known hardness to scratch the stone with. You can use a material such as glass, porcelain tile, or a knife to scratch the stone. Or, you can acquire a scratch test kit containing tools for performing the test. If you elect to use the scratch test kit, your tool will have the hardness listed. If you use the method of using one material to scratch another, you will need to know the hardness of the test material.

Take the tool and try to scratch the stone with it using significant force. If the tool scratches the stone, then the tool is harder, if the tool does not scratch the stone then the stone is harder. Use various tools of varying hardness until you have determined at which hardness the stone begins to be scratched.

Why is the hardness of stone significant? Because it contributes to the durability of the material. The more scratch resistant the stone is, the more durable. The more durable, the longer it will last. The harder stones are normally of the siliceous type. Some of these include:

  • Granite
  • Quartzite
  • Sandstone
  • Serpentine
  • Gneiss (Commercially Called Granite)

What These Tests Reveal

After you have performed these tests, the results give you vital information that you can use to identify the stone you actually have. Knowing if the stone is calcareous or siliceous coupled with how hard the slab is can give you an indication of what stone your slab is.

For example, some slabs which are labeled "quartzite" have proven to contain a significant amount of calcite (calcium carbonate). Since quartzite is a siliceous stone (geologically speaking), slabs labeled this way then, could not be viewed as true quartzite. This is the kind of thing that is good to know when purchasing a slab.

The porosity of a slab gives you an idea of the density. Density contributes to the durability in a way similar to the scratch test. Dense stone resists chipping and staining better than porous materials.

Getting to know your stone by testing it is the most reliable way to understand how it will last and perform. The tests we have talked abut in this article help you to do that. Most fabricators can help you to determine what the slab is called. Yet these test can assist you in verifying the naming convention used for a particular slab. So, remember these tests. They may come in handy.