An abrasive is any material used to grind, cut, polish, or remove surface material from another substance. This function relies on the abrasive being harder than the material it is working on, essentially scratching it away at a controlled rate. The most commonly and widely used naturally occurring mineral abrasive, due to its exceptional abundance and cost-effectiveness, is Quartz, also known as silica. Quartz is a fundamental component of sand and sandstone, making it readily available for large-scale industrial applications.
Understanding Mineral Hardness
The effectiveness of any mineral abrasive is governed by its ability to resist scratching, measured using the Mohs Scale of Mineral Hardness. Developed in 1812 by Friedrich Mohs, this ordinal ranking compares the scratch resistance of ten common minerals. A mineral can scratch all others lower on the scale but will be scratched by any mineral ranked higher. The scale ranges from Talc (1) to Diamond (10), the hardest natural material. This non-linear scale means the difference in absolute hardness increases significantly toward the top.
The Most Widely Used Mineral Abrasive
The mineral most frequently employed as an abrasive in industrial and consumer settings is Quartz, which is composed of silicon dioxide (\(\text{SiO}_2\)). Its widespread use stems from its status as the second most abundant mineral in Earth’s crust, ensuring a nearly inexhaustible and low-cost supply. Quartz has a hardness of 7 on the Mohs scale, which is hard enough to scratch most common materials like steel, glass, and iron, making it highly versatile for general use.
Quartz sand, or silica sand, is the material of choice for large-volume applications such as sandblasting and general scouring cleansers. Its crystalline structure naturally fractures into sharp, angular fragments, providing the necessary cutting edges for effective abrasion. The durability of quartz also means it resists chemical and physical weathering, which allows it to maintain its abrasive qualities during processing.
Finely ground silica is incorporated into products like sanding grits and specialized compounds for polishing glass and metals. While its use in sandblasting has declined in some regions due to health concerns related to silicosis, its abundance and hardness ensure it remains the dominant mineral abrasive for many bulk and low-cost applications globally.
Higher Grade Mineral Abrasive Materials
While quartz is the most common bulk abrasive, other naturally occurring minerals are used when higher performance, greater purity, or specific properties are required. Garnet is one such mineral, boasting a Mohs hardness typically ranging between 7.5 and 8, which is slightly harder than quartz. The unique, sharp, and angular grain shape of garnet, coupled with its relatively low dust generation, makes it the preferred abrasive for specialized sandblasting and marine applications.
Garnet is also highly effective for waterjet cutting, where a fine, consistent abrasive stream is necessary to slice through materials like metal and stone. Corundum, natural aluminum oxide (\(\text{Al}_2\text{O}_3\)), ranks at 9 on the Mohs scale and is significantly harder than both quartz and garnet. This extreme hardness allows corundum to be used in precision grinding wheels, coated abrasives like sandpaper, and tooling for manufacturing.
At the top of the natural hardness scale is Diamond, with a Mohs rating of 10. Diamond grit is reserved for the most demanding applications, such as cutting and grinding extremely hard materials like ceramics, concrete, and superhard alloys. It is often used in specialized drill bits and saw blades, where its unparalleled hardness ensures tool longevity, justifying its higher cost.