Quartz is a widely occurring mineral, forming a fundamental component of various rocks and sands. This article explores quartz’s notable property of hardness, examining its capacity to scratch other materials and its susceptibility to being scratched itself.
Understanding Mineral Hardness
Mineral hardness refers to a material’s resistance to scratching or abrasion, a property distinct from its toughness or resistance to breaking. Geologists and material scientists commonly use the Mohs scale of mineral hardness to quantify this characteristic. This qualitative scale, ranging from 1 to 10, ranks minerals based on their ability to scratch one another.
A mineral higher on the Mohs scale can scratch any mineral lower on the scale. For instance, talc, rated as 1, is the softest mineral. Diamond, with a rating of 10, is the hardest known natural mineral and can scratch any other substance.
Quartz’s Place on the Mohs Scale
Quartz holds a specific position on the Mohs scale of mineral hardness, rated at 7. This numerical value signifies that quartz is relatively hard, capable of resisting scratches from many common materials. However, it is not at the top of the scale, indicating that harder substances can still mark its surface. This placement makes quartz a benchmark for assessing the hardness of other minerals.
Its Mohs hardness of 7 means quartz is harder than most metals and many other minerals. This property contributes to its durability and widespread use in various applications.
Materials Quartz Can Scratch
Given its Mohs hardness of 7, quartz can scratch a wide array of softer materials. One common material quartz can scratch is glass, which typically has a Mohs hardness ranging from 5.5 to 6.5. This explains why sand, largely composed of quartz grains, can abrade and etch glass surfaces over time.
Many common metals also fall below quartz on the hardness scale. Steel, for instance, generally has a Mohs hardness between 5 and 6.5. Consequently, quartz can scratch steel tools or surfaces. Softer metals like copper (Mohs 2.5-3), aluminum (Mohs 2.5-3), and iron (Mohs 4-5) are also readily scratched by quartz.
Numerous minerals are susceptible to scratching by quartz. Examples include calcite (Mohs 3), fluorite (Mohs 4), apatite (Mohs 5), and feldspar (Mohs 6-6.5). Even certain types of granite, which contain minerals softer than quartz, can be scratched by pure quartz. This makes quartz a useful tool in mineral identification, as it can test the hardness of unknown samples.
Materials That Can Scratch Quartz
While quartz is notably hard, it is not impervious to all materials. Any substance with a Mohs hardness greater than 7 can scratch quartz. Minerals such as topaz (Mohs 8) can leave a mark on quartz. Corundum, encompassing varieties like ruby and sapphire, has a hardness of 9 and can easily scratch quartz surfaces.
The hardest naturally occurring mineral, diamond (Mohs 10), will readily scratch quartz. Industrial abrasives often incorporate these harder materials to cut or polish quartz. While quartz is durable for many everyday uses, it remains vulnerable to damage from these much harder substances.
Everyday Implications
The inherent hardness of quartz has significant implications for its everyday uses and interactions. Its resistance to scratching makes it a popular choice for kitchen countertops, where durability against daily wear and tear is desirable. Similarly, quartz is often incorporated into jewelry due to its ability to maintain its luster and resist abrasions from common environmental factors.
The prevalence of quartz in sand also explains why seemingly innocuous dust can scratch softer surfaces like car paint or smartphone screens. Understanding quartz’s hardness helps in selecting appropriate cleaning methods and protective measures for various materials.