There are a lot of questions, rumors, myths, and misinformation about the hardness of soapstone. I’d like to inform you about the facts of this stone, its characteristics, its hardness and uses, and how to test it so you are fully informed about this durable, natural material.
Soapstone Mineral Composition and Uses
Since soapstone is made mostly of talc, it is naturally softer than many stones. What determines its hardness or softness comes down to how much talc is present among other minerals in soapstone’s composition. Average architectural grade soapstone contains approximately 50% talc and is commonly used for countertops, wood burning stoves, sinks, and floor tiles. This composition is also called steatite. Harder soapstone is likely 30% talc, while softer stone—used by the art industry for carvings and other installations—will often have 80% talc in its mineral makeup.
Differences Between Soapstone and Serpentinite
There are natural stones falsely labeled as soapstone that fail to meet one very important requirement: talc content. Some very hard “soapstone” has no talc in it, and in petrological terms, it cannot be called soapstone; it is serpentinite.
I have heard references to the “new generation” of soapstone being harder; this is comical because in geological terms, serpentinite metamorphosed into soapstone, which makes these harder stones the “old generation,” and the softer soapstone you know today is its new iteration.
How does an average person tell soapstone from serpentinite? Testing the stone’s hardness is a common characteristic to measure. If a stone is so hard that it cannot be scratched with a knife blade, chances are that it is a serpentinite and not a true soapstone.
Serpentinite hardness isn’t the only characteristic that makes it different from soapstone. It also differs in its thermal properties. While one cannot use serpentinite in an application with extreme heat, soapstone boasts heat retention and durability in excessive temperatures including fireplace linings and mantels.
Measuring Mineral Hardness With Mohs’ Scale
Mohs’ scale of hardness is one way to determine the actual hardness of soapstone. Although Mohs’ scale was classified using 10 basic minerals (not rocks or stones), it can be used as a guideline to determine the hardness of all materials, including soapstone.
To determine where any material falls on the Mohs’ scale of hardness, it needs to be tested against a mineral on the scale. As an example, a fingernail cannot scratch Calcite (3) but it will scratch Gypsum (2), so it can be concluded that a fingernail is approximately a 2.5 on the scale.
With that mode of comparison in mind, if you scratch soapstone with something that has a confirmed hardness and the soapstone scratches, we know it is the softer material and we can begin to make additional comparisons to rank the stone. We’ve provided some hardness values for common materials below for your own use to see the actual hardness of soapstone or other materials.
- Fingernail: 2.5
- Copper penny: 3.5
- Knife blade: 5.5
Keep in mind that anything harder than the knife blade is definitely a serpentinite and not a soapstone.
Is Soapstone Fragile?
No, soapstone is not fragile. Even though it is softer than other stones, namely serpentinite, the mineral makeup creates a pliable material that isn’t brittle or susceptible to cracking. Its various grades make soapstone adequate for many uses, from artistic carvings to outdoor furniture, countertops, and floor tiles.
Does Soapstone Scratch Easily?
Most soapstone will only scratch if one purposely tries to damage the stone; how easy it is to scratch depends on the grade—how much talc is present—and the softness of the stone. If your stone does become scratched, the beauty of it is that you can easily buff the area with regular sandpaper or apply a dab of mineral oil or soapstone wax to hide the scratch; this easy fix is one of its distinctive features.
Explore more soapstone facts and tips at our blog. Thanks for reading,
Rogerio M. Teixeira