The Mohs scale and the hardness of petrified wood
The hardness of a material says a lot about how well it resists scratches, wear, and damage. In the world of natural stone, this is often referred to as Mohs scale Used: a simple but effective method for determining the scratch resistance of minerals. In this blog post, we explain how the Mohs scale works and what this means for its use and maintenance of petrified wood.
🔢 What is the Mohs scale?
The Mohs scale was developed in 1812 by the German mineralogist Friedrich Mohs. He established a ranking of ten common minerals, each of which can scratch the previous one but not the next. This creates a relative hardness scale from 1 (very soft) to 10 (very hard):
- Talk
- Plaster
- Calcite
- Fluorite
- Apatite
- Orthoclase (feldspar)
- Quartz
- Topaz
- Corundum
- Diamond
For example, a stone with hardness 6 can scratch fluorite (4), but not quartz (7).
🌳 How hard is petrified wood?
Petrified wood consists largely of silicon dioxide (SiO₂), the same mineral that also quartz consists of. During the fossilization process, the pores and cells of the wood are slowly filled with silica, which eventually turns it into a rock-hard mineral. The hardness of petrified wood is therefore almost always between 6,5 and 7,5 on the Mohs scale.
This means that petrified wood:
- Harder than steel (usually 4-5 on the Mohs scale),
- Scratch resistant is with normal use,
- And comparable to materials such as granite or quartzite.
Not every piece of petrified wood is exactly the same hardness. This depends on the degree of mineralization, the type of minerals that fill the wood (e.g., chalcedony, jasper, or opal), and the origin.
✅ Benefits of high hardness
The high hardness of petrified wood has clear advantages:
- Scratch resistant: You can safely place a cup or bowl on it without fear of scratches.
- Wear-resistant: It remains beautiful for years, even with intensive use.
- Hygienic: Thanks to the dense, hard structure, dirt and bacteria have virtually no chance to adhere.
- Suitable for indoor and outdoor use: Think of tables, wash basins, windowsills or gravestones.
⚠️ Disadvantages and points of interest
While the hardness is an advantage, it also has a downside:
- Brittleness: Hard material is often less flexible. Petrified wood can break in case of a hard blow or fall. crack or break.
- Not flexible to process: You can't just saw or drill it without professional tools.
- Heavy: The dense structure makes petrified wood quite heavy, which can make transport or installation more difficult.
- Uneven hardness: Stonemasons and processors sometimes find petrified wood difficult to work with because it's not consistently hard throughout. In some areas, it drills surprisingly easily, while in others, the drill almost bounces or sparks. This is because petrified wood is composed of various minerals with varying density and structure.
Tool tip: To work with petrified wood, you need professional diamond tools. Preferably use wet sawing or drilling tools to prevent overheating and cracking. Regular drill bits or saw blades are unsuitable and easily damaged.
That is why it is important to treat petrified wood with care and, for example, not to drop it on a hard surface.