The Mohs Scale Explained – Understanding Hardness in Crystals
Identifying minerals can be surprisingly challenging. While many crystals and minerals have distinct visual properties that aid identification, this isn’t true for all.
That’s where the Mohs hardness scale comes in. A simple, practical and enduring geological method for determining a mineral or crystal’s resistance to scratching or abrasion, it has been used for over 200 years to help identify minerals from around the world.
At Fossils UK, we have a fascination for all things geology. In this article, we will discuss the origins of the Mohs scale, why it’s used, if it’s still relevant and how it can help you as you develop your crystal collection. Ready to enhance your mineral identification skills? Read on and expand your expertise with our comprehensive guide.
Table of contents
- What is the Mohs hardness scale?
- Breaking down the Mohs scale
- Is the Mohs hardness scale still accurate?
- Why does hardness matter for crystals?
- Shop stunning crystals at Fossils UK
What is the Mohs hardness scale?
The Mohs hardness scale is one of the most widely recognised tools in mineralogy. Developed in 1812 by the German geologist and mineralogist Friedrich Mohs, this scale measures the hardness of a mineral by comparing it to the hardness of other minerals. Rather than using specific units of measurement, the scale assigns minerals a value between 1 and 10 based on their ability to scratch other minerals or be scratched.
The origins of the Mohs hardness scale trace back to Mohs’ work in identifying minerals, which led him to realise that certain minerals could be ranked by their ability to resist scratching.
The scale begins with the softest mineral, talc (ranked as 1), and progresses to the hardest, diamond (ranked as 10). By using common minerals of varying hardness, Mohs created a simple method for geologists and mineral collectors to assess and differentiate between a wide array of minerals based on their scratch resistance.
Breaking down the Mohs scale
The Mohs scale is divided into ten levels, with each mineral assigned a number based on its ability to scratch the one below it. The most common minerals at each level are as follows:
| Rank | Mineral | Hardness |
| 1 | Talc | Very soft, can be scratched by a fingernail |
| 2 | Gypsum | Can be scratched with a fingernail |
| 3 | Calcite | Can be scratched by a copper coin |
| 4 | Fluorite | Can be scratched by a knife |
| 5 | Apatite | Can be scratched by a knife or steel file |
| 6 | Orthoclase | Can scratch glass |
| 7 | Quartz | Can scratch steel |
| 8 | Topaz | Can scratch quartz |
| 9 | Corundum | Includes sapphires and rubies |
| 10 | Diamond | The hardest mineral known, can scratch all others |
Each mineral in the table above is ranked based on its ability to scratch the one below it, meaning a mineral ranked 6 (Orthoclase) can scratch any mineral ranked 5 (Apatite) or lower, but will be scratched by minerals ranked 7 or higher (such as Quartz).
This simple ranking system enables a quick comparison of hardness between minerals and helps determine the identity of unknown minerals. In practice, geologists will often carry a set of test minerals, such as a steel file, a copper coin, and a piece of quartz, to test the hardness of a specimen in the field.
Is the Mohs hardness scale still accurate?
Although the Mohs scale has served the geological community well for over two centuries, it’s not without its limitations. The scale is subjective. Determining whether one mineral can scratch another depends on the precision of the test and can vary based on factors such as surface roughness or impurities within the minerals.
However, despite these drawbacks, the Mohs scale remains the go-to method for fieldwork and basic mineral identification. This is because it’s practical, easy to use, and effective for distinguishing between a wide range of minerals without the need for advanced equipment.
In the world of geology, various methods exist for determining hardness (such as the Vickers and Knoop scales), but the Mohs scale’s long-standing reliability means it remains the preferred tool for field identification. It also serves as an excellent introduction for those new to mineralogy, providing a clear starting point for further learning.
Why does hardness matter for crystals?
Hardness is a fundamental property of crystals and minerals that has far-reaching implications in both scientific and practical contexts. For scientists, accurately determining the hardness of a crystal can help identify its structure, origin, and potential applications. For example, a mineral’s hardness often correlates with its molecular structure, and the Mohs scale can provide valuable clues about its crystallography.
For collectors, understanding the hardness of a crystal is essential for preserving their specimens. Minerals that rank lower on the Mohs scale are more prone to scratching, which can diminish their appearance and value. Conversely, harder minerals are more durable and resistant to damage. For example, if you’re handling a specimen of calcite (hardness 3), you’d need to take extra care to avoid scratching it with harder objects.
The Mohs scale also plays a key role in industries that rely on minerals for their physical properties. For example, diamond, with a hardness of 10, is used in cutting tools, while softer minerals, such as talc, are commonly used in cosmetics and pharmaceuticals.
When it comes to crystals specifically, knowing a mineral’s hardness helps collectors choose appropriate settings for display or wear, ensuring that their crystals are both protected and showcased to their best advantage. It also helps prevent accidental damage when handling delicate specimens, ensuring that the beauty and integrity of the crystals are maintained.
Shop stunning crystals at Fossils UK
Now that you have a deeper understanding of the Mohs scale and how it relates to crystal identification, why not take a closer look at the incredible collection of crystals at Fossils UK? Whether you’re a budding collector or an experienced enthusiast, our range of stunning, high-quality crystals is sure to impress.
At Fossils UK, we source only the best specimens from around the globe, ensuring that each crystal is authentic and unique. From delicate amethyst geodes to striking quartz formations, we have something for every taste and collection. Our online store makes it easy to browse and shop for crystals that will complement your growing collection.
Browse our full range of crystals and crystal gifts today to build your own collection, or help a loved one develop theirs.
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