Quartz is harder than glass, a distinction rooted in their fundamental differences in atomic structure and resistance to scratching. Quartz is a natural mineral, often found as a transparent or translucent crystal. Glass is typically a manufactured solid, made by rapidly cooling a molten mixture of silica and other compounds before it can crystallize. This structural difference accounts for the variation in the physical strength of the two materials.
Understanding the Mohs Scale of Hardness
The most common method for measuring the scratch resistance of a material is the Mohs scale of hardness. Hardness is defined by a material’s ability to resist permanent deformation, specifically scratching or abrasion. The scale, developed in 1812, is a qualitative and relative measure that ranks minerals from one to ten.
This ranking system is based on the principle that a harder material will scratch a softer one. The Mohs scale uses ten reference minerals, with talc at one and diamond at ten, to create a comparative standard. The scale is not linear; the jump in absolute hardness between a nine and a ten is much greater than the jump between a one and a two.
Direct Comparison: Quartz Versus Common Glass
Quartz, in its natural mineral form, is rated as a 7 on the Mohs scale of hardness. Common manufactured glass, such as the soda-lime glass used in windows and beverage bottles, typically falls within a Mohs hardness range of 5.5 to 6.0. This difference explains why quartz will easily scratch ordinary glass. Sand, which is largely composed of quartz, can damage glass surfaces over time through abrasion. While some specialized forms of glass can approach or even exceed a 7, the vast majority of everyday glass remains significantly softer than quartz.
Crystalline Structure Versus Amorphous Structure
The primary reason for the hardness difference lies in the internal arrangement of the silicon dioxide (SiO2) molecules that make up both materials. Quartz is a crystalline solid, meaning its atoms are arranged in a highly ordered, three-dimensional, repeating lattice structure. This regular, tightly-bonded atomic framework requires substantial energy to break, giving the material its high scratch resistance.
In contrast, common glass is an amorphous solid, often described as a supercooled liquid because its atoms are arranged in a continuous but random network. Although glass is also composed primarily of silicon dioxide, the lack of a long-range, repeating structure creates inherent weaknesses. This disordered structure makes it easier for a sharp point, like quartz, to penetrate and cleave the weaker areas of the network. The crystalline lattice of quartz resists this penetration much more effectively than the amorphous structure of glass.