In short. An N grade counts the nines in the SiO2 percentage: 3N means three nines, 5N means five. That figure is usually calculated by difference, so it depends on which impurities were measured and by which method. For a buyer, the individual elements and batch-to-batch consistency matter more than the grade.
Quartz is often sold by a grade written as a count of nines. It is a useful shorthand. It is also easy to misread.
What the N number means
| Grade | SiO2 | Total impurities |
|---|---|---|
| 2N | 99% | 10,000 ppm |
| 3N | 99.9% | 1,000 ppm |
| 3N5 | 99.95% | 500 ppm |
| 4N | 99.99% | 100 ppm |
| 4N5 | 99.995% | 50 ppm |
| 5N | 99.999% | 10 ppm |
SiO2 is usually calculated, not measured
For high-purity material, laboratories usually report SiO2 by difference. They measure a list of impurity elements and subtract the total from 100%. The result depends on which elements were on the list. Leave out the ones that matter for your application and the SiO2 figure rises without the quartz changing at all.
The method sets the floor
X-ray fluorescence (XRF) is fast and common for major oxides, but its detection limits are too high to confirm impurity levels in the low parts-per-million range. Plasma methods, ICP-OES and ICP-MS, measure trace elements much lower. A 4N or higher claim that rests on XRF alone deserves caution. Ask for the method and the detection limit behind every figure.
Individual elements matter more than the total
Two lots with the same N grade can behave very differently. Iron tints glass. Alkalis such as sodium, potassium and lithium lower the viscosity of fused silica and encourage devitrification at high temperature. Boron and phosphorus matter in silicon because they act as dopants. Aluminium and titanium often sit inside the crystal lattice, where processing cannot reach them. A useful specification sets a limit for each element, not only a total.
Consistency matters more than peak purity
For a production line, a stable impurity profile across shipments is worth more than one exceptional result. A furnace, a glaze recipe or a resin formulation is tuned to its raw materials. When the feedstock drifts, the process drifts with it. Ask for results across several batches, not the best one.
What we report
We supply industrial quartz feedstock, and we report measured values rather than an N grade. Each commercial batch comes with a Certificate of Analysis covering SiO2, selected impurity elements and particle-size distribution.
Revised September 2026 to separate industry background from what quartz.lk supplies.
