Natural Stone Hardness, Staining & Marble Sub-Groups
We often see our natural stone options as specific groups of stone: Marble, Granite, Quartzite. However, it may be best to see them as a spectrum of options!
In general, the Mohs Hardness Scale is as follows: Soapstone 1 · Slate 2.5-4 · Calcite 3 · Marble 3-4 · Dolomite 3.5-4 · Limestone 3-4 · Travertine 4-5 · Sandstone 6-7 · Granite 6-7 · Quartzite 7 · Diamond 10
Let's Take a Closer Look, with an Emphasis on Brazilian Stone, a major stone source.Granite - Resistant to stain or etch, but some can scratch, specially the ones with black mineral called mica (or schist), such as Black Mist, Brazilian Black and Black Thunder. A leather or honed finish, should minimize the scratching problems. Some black granite such as Saturnia are actually all made of the mica mineral and because of that they usually scratch easier. Some others such as Titanium and Magma also have some mica, but much less than Saturnia, so it won’t strach as easy.
Quartzite - these are some of the hardest stone mother natural can produce. They are all made of natural quartz and because of that it won’t scratch at all. However, some of them can absorve water and other liquids, such as the most white colors for example Bianco Superiore, Lavezzi, Mustang White and White Lux. However, once we are done polishing the slabs, we apply our sealer which should protect those materials from absorbing water. The problem is that when a fabricator cuts the stone and edges that sealer can go away at those areas where they were cut. So the fabricator will need to wait until it’s fully dry and then add a sealer again before installing. That way it should avoid the water absorption problem.
Marble - classifying Brazilian Marbles into three categories:
1. Regular Marble - this would be similar to any known marbles worldwide. It’s softer and more fragile, which makes of it good options for bathrooms, lower traffic uses, best care situations, since they can scratch and stain easier. Very few Brazilian Marbles can be classified into regular marbles. Some of the regular marbles from Brazil are: Amazon, Arctic Green, Mandala (or Avalanche), Carrara Brazil, Sequoia Brown and a very few others.
2. Dolomitic Marble
Most of Brazilian marbles are actually Dolomitic Marbles. Dolomite is a mineral that makes the Brazilian marbles much more resistant to wear. It usually does not scratch or stain easily and that’s why some confuse it with a quartzite. It’s actually a very hard marble an maybe it shouldn’t even call it marble. The main issue you can have with these stones is etching. It can etch with acids (lemon, etc) and when it does, the polished surface will become duller. If the surfaces is honed or leather finished, one is much less likely to notice when it etches, since these finishes are somehow already etched! This is why most of the Brazilian slabs have honed, leather or even dual finished (back honed and front polished) options. Most Brazilian marbles are dolomitics. They include: Aspen White, Tesoro Bianco, Aurelius White, Fantastic Brown, London Fog, Matarazzo, Manhattan, Panda, Shadow Storm, Silver Cloud, Supreme White, Super White and many others.
3. Dolomitic Marble with Calcite Mineral
These stones contain some natural crystals called calcite. Calcite crystals are super hard and highly etch resistant. However these crystals can be tricky to edge as it can crumble a bit when cutting during fabrication. Most fabricators are fine if they run a straight edge on it when cutting. These minerals are translucent, which makes a nice for backlit tops in kitchens, bathroom and bar tops. Some stone colors from this category are: Ice Crystal, Blue Iceberg and White Cloud.
In closing, the properties of Brazilian Dolomitic Marbles may change how we view our kitchen countertop options. These materials are clean looking, very unique, with a modern appeal.
Sources & Learn More
Brother In Granite of Brazil (Special thanks to Fernando)