Quartz in Composites and Engineered Stone: Filler Ratio, Hardness and Aesthetics
Quartz is the core filler that makes up most of engineered stone (quartz countertops) and composite materials by weight, giving hardness, whiteness and durability. We explain the role of granular and micronised quartz in composites, the filler ratio and the selection criteria.
Quartz is the core filler material that makes up most of engineered stone (quartz countertops, artificial marble) and engineering composites by weight. Thanks to its high hardness, whiteness and chemical stability, it gives the final product both mechanical strength and aesthetics. In this article we explain the role of quartz in producing composites and engineered stone, how granular and micronised grain sizes are used together, and the criteria by which the right quartz is selected.
The Role of Quartz in Engineered Stone
Engineered stone is produced by binding quartz aggregate and powder with a resin (usually polyester) and pressing the mixture. In the product, quartz is not merely a filler but the main component that defines the product's character:
- Hardness and scratch resistance: With a hardness of Mohs 7, quartz gives the countertop surface high resistance to scratching in everyday use.
- Mechanical strength: A high filler ratio provides impact and flexural strength in the product.
- Whiteness and colour control: A low iron (Fe₂O₃) content means high whiteness, which is critical when producing countertops that require light colours and a uniform tone.
- Chemical stability: Because SiO₂ is inert, the surface withstands food acids and cleaning chemicals.
- Dimensional stability: Low thermal expansion helps the panel keep its shape.
Granular or Micronised? Grain Size Distribution
Engineered stone and composites use not a single grain size but a granulometric distribution, which allows a high filler ratio and low resin consumption:
- Granular quartz (0.5–2 mm): the coarse aggregate that forms the product's skeleton and volume, providing mechanical strength and texture.
- Micronised quartz (< 45 µm): the fine powder that fills the gaps between the coarse grains, providing surface smoothness, homogeneity and a higher filler ratio.
Using the coarse and fine fractions together yields a composite with less resin and more quartz — that is, harder and more durable. For details, see our engineered stone application page.
Technical Properties
The key values of the quartz used in composites and engineered stone:
| Property | Granular Quartz | Micronised Quartz |
|---|---|---|
| SiO₂ purity | ≈ 99.8% | ≈ 99.8% |
| Iron (Fe₂O₃) | ≈ 0.013–0.019% | ≈ 0.013% |
| Hardness | Mohs 7 | Mohs 7 |
| Density | 2.65 g/cm³ | 2.65 g/cm³ |
| Grain size | 0.5–2 mm | < 45 µm |
In both products, high SiO₂ purity and low iron provide both strength and whiteness in the composite. The values are typical batch values; a current batch analysis report is provided with each shipment.
Why Quartz Instead of Calcite in Composites?
In composite fillers, the biggest advantage of quartz over calcite or marble powder is its hardness: quartz is Mohs 7, while calcite is only Mohs 3. This difference is decisive for scratch resistance and service life in countertop and surface applications. Quartz's chemical stability also increases the surface's resistance to stains and acids. For this reason, quartz is the material of choice in high-performance engineered stone and engineered surfaces.
Why Silis Kum?
Our granular and micronised quartz is processed at our own facilities in the Thrace region and classified with a controlled grain distribution. We can define together the fractions your composite formula requires, and you can receive an analysis report for each batch and a free sample before you decide. Get in touch with us.