What is the Mohs Hardness Scale?
The Mohs hardness is a comparative method to measure the scratch resistance of a material. The idea behind the Mohs hardness scale is quite simple. The Harder material scratches the softer material.
The Mohs hardness scale is based on a scale of 1 to 10, with diamond being the hardest material with a top value of 10. Materials are tested against each other, and if one scratched the other, it would give the material a higher value.
For example, gypsum can scratch talc; therefore, it has a higher Mohs value than talc.
Understanding Mohs Hardness
The science of mineralogy owes much of its understanding to various scales and measurements that have been devised over the years. One such key scale, which gauges the hardness of minerals, is the Mohs Hardness Scale. For anyone with an inclination towards gemology, geology, or mineralogy, this scale offers an invaluable tool to differentiate and categorize minerals. Let's delve deep into understanding the Mohs Hardness.
Origins of the Mohs Scale
The Mohs Hardness Scale was conceived in 1812 by Friedrich Mohs, a German geologist and mineralogist. Recognizing a need to classify minerals in some kind of systematic order, he devised a simple, yet effective, method of determining hardness. This involved observing which minerals could scratch others.
It's fascinating to note that Mohs didn’t invent the concept of hardness testing. Ancient civilizations had already made observations about which materials could be used to scratch or carve into others. Mohs, however, was the first to compile a consistent and comparative list.
Mohs hardness scale
| Hardness | Material |
|---|---|
| 1 | Talc |
| 2 | Gypsum |
| 3 | Calcite |
| 4 | Fluorite |
| 5 | Apatite |
| 6 | Orthoclase feldspar |
| 6,5 | Borosilicate Glass |
| 7 | Quartz |
| 7 | Impactinator® Glass |
| 8 | Topaz |
| 9 | Corundum |
| 9 | Sapphire Glass |
| 10 | Diamond |
Applications and Relevance
Gemology and Jewelry: One of the immediate applications of the Mohs Scale is in gemology. When designing jewelry, it's imperative to understand the hardness of the gemstones being used, since it directly impacts their durability and resistance to abrasion. For instance, diamonds, with a Mohs hardness of 10, are often used in engagement rings because they resist scratching better than most other stones.
Construction and Manufacturing: The hardness of materials plays a pivotal role in construction and manufacturing industries. For instance, understanding the hardness of minerals can help in selecting the right kind of machinery or tools for mining or cutting.
Education: The Mohs Scale serves as an elementary tool for introducing students to the world of mineralogy. Its simplicity and ease of use make it a favorite among educators.
Limitations of the Mohs Scale
The Mohs hardness scale is easy to use, but it lacks accuracy because of only 10 scales, with a near logarithmic relationship to absolute hardness. A difference of Mohs Hardness of 5 and 6 cannot be truly determined and is more of an approximation than the more sophisticated and high precision hardness measuring methods like Vickers or Rockwell.
Relative Hardness: The Mohs Scale measures only relative hardness. It doesn’t provide an absolute or quantitative measure. For instance, while diamond is ranked 10 and corundum 9, diamond is actually many times harder than corundum. Lack of Precision: The scale lacks intermediate values. Hence, if two minerals fall between two numbers, determining their relative hardness can be challenging. Not Comprehensive: The scale covers only 10 minerals. Many minerals fall in between these standard numbers, requiring the use of additional reference minerals. Other Hardness Measurements
Given the limitations of the Mohs Scale, other methods have been developed for a more precise measurement of hardness. The Vickers and Rockwell scales, for instance, measure hardness by assessing the depth or size of an indentation left by a fixed force. These scales are more commonly used in metallurgy.
Advantages of the Mohs Scale
The advantage of the Mohs hardness measuring method is the scratching process compared to the denting of the other two methods. This is especially useful for crystalline materials like glass or ceramics that will shatter and not deform.
It is a easy quick and cost effective method to determine the scratch hardness of minerals. A Test kits costs less the 30 USD. And before you ask. Such a low cost test kit comes without a real diamond.
Conclusion
The Mohs Hardness Scale, despite its limitations, remains a cornerstone in the world of mineralogy. Its simplicity, ease of use, and the fact that it requires no special equipment make it widely popular. Whether it's used by a student in a classroom, a jeweler assessing gemstones, or a geologist in the field, the Mohs Scale stands as a testament to Friedrich Mohs' ingenuity and the enduring importance of systematic classification in science.
