What Is Quartz? A Complete Guide for Spectroscopy & Optics (2026)
Quartz is a crystalline form of silicon dioxide (SiO₂) — the second most abundant mineral in the Earth’s crust and one of the most useful natural materials in science. Pure quartz is colorless, transparent, has a hardness of 7 on the Mohs scale, and exhibits piezoelectric properties. In optics and spectroscopy, the term “quartz” most often refers to fused quartz (synthetic amorphous SiO₂), which transmits light from 170 nm (deep UV) through 3,500 nm (mid-IR), withstands temperatures up to 1,100 °C, and has the lowest thermal expansion of any commercial optical material (0.55 × 10⁻⁶/K). These properties make quartz the standard substrate for UV-Vis cuvettes, semiconductor wafer carriers, photolithography masks, laser optics, and high-temperature labware. Last updated: June 2026.
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Why trust this guide? MachinedQuartz LLC has been working with quartz optical components since 2013. This guide reflects ASTM, ISO 11104, and NIST reference data for spectrophotometry, plus our internal QC standards for cuvettes and optical windows shipped to 30+ countries.
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What is quartz?
Quartz is a hard, crystalline mineral made of one silicon atom bonded to two oxygen atoms — chemical formula SiO₂. It is the second most abundant mineral in the Earth’s continental crust after feldspar, making up around 12% of all crustal rock. Pure quartz is colorless and transparent, but trace impurities give us amethyst (purple), citrine (yellow), rose quartz (pink), and smoky quartz (gray to black). For science and industry, however, “quartz” almost always means one of two specific forms:
- Natural crystalline quartz — mined as single crystals, used as a feedstock for melting
- Fused quartz (also called fused silica) — synthetic amorphous SiO₂ produced by melting high-purity natural quartz or by chemical vapor deposition
When a spectrophotometer datasheet says “use a quartz cuvette,” it means a cell made from fused quartz, not a polished crystal. The distinction matters for transmission, thermal performance, and how the material behaves in the cuvette manufacturing process. We cover that distinction in detail in the next section.
Natural quartz vs fused quartz
Crystalline Quartz
Regular trigonal lattice — naturally mined, birefringent. Not used for cuvettes.
Fused Quartz (Amorphous)
Random SiO₂ network — synthetic, isotropic. Used for cuvettes and optics.
Cuvette Form
Cut, polished, sealed from fused quartz blocks. 1–100 mm path lengths.
| Property | Natural Crystalline Quartz | Fused Quartz (Synthetic) |
|---|---|---|
| Structure | Crystalline (trigonal) | Amorphous (glassy) |
| Source | Mined from quartz veins | Melted from quartz sand or made from SiCl₄ vapor |
| Purity | 99.5–99.9% SiO₂ | 99.99% – 99.9999%+ SiO₂ |
| Birefringence | Yes (double-refracts light) | No (isotropic) |
| UV transmission | Limited by impurities | Down to 170 nm (deep UV) |
| Used for cuvettes? | No | Yes — all quartz cuvettes are fused |
Birefringence is the deciding factor for optics: a crystalline quartz cell would split a beam in two, ruining absorbance measurements. Fused quartz is isotropic — light passes through it the same way in any direction — which is why every quartz cuvette and optical window on the lab market is made from fused quartz, never from natural crystal.
Key physical & optical properties
What makes fused quartz uniquely valuable is the combination of five properties no other commercial material matches simultaneously:
| Property | Value | Why it matters |
|---|---|---|
| Density | 2.20 g/cm³ | Lighter than borosilicate (2.23) or soda-lime (2.50) |
| Coefficient of thermal expansion | 0.55 × 10⁻⁶/K | ~15× lower than borosilicate — survives thermal shock from red heat to ice water |
| Maximum service temperature | 1,100 °C continuous, 1,200 °C short | Highest of any commercial optical glass |
| Softening point | 1,683 °C | Stays rigid where borosilicate (820 °C) deforms |
| Refractive index (at 589.6 nm) | 1.4585 | Predictable Fresnel reflection losses (~7% per surface) |
| UV-Vis-NIR transmission | 170 – 3,500 nm | Covers deep UV through mid-IR with one material |
| Hardness (Mohs) | 5.3 – 6.5 (fused), 7.0 (crystalline) | Scratch-resistant in normal lab handling |
| Chemical resistance | Inert to all acids except HF | Survives nitric, sulfuric, perchloric — etched only by HF and hot phosphoric |
| Dielectric strength | 250–400 kV/cm | Excellent electrical insulator at any temperature |
The combination above is why fused quartz is the only choice for UV-Vis spectroscopy cuvettes, semiconductor diffusion tubes, photomask blanks, and high-power laser windows. No competing optical material — not borosilicate, not soda-lime, not BK7, not even sapphire — covers this entire envelope.
JGS1, JGS2, JGS3 — the three quartz grades
Schematic transmission curves — JGS1 reaches 170 nm but drops at 2,730 nm OH band; JGS3 has no OH band, reaches 3,500 nm.
Fused quartz is sold in three optical grades distinguished by manufacturing route, OH (hydroxyl) content, and useful spectral range. The grade choice determines whether your application is feasible — getting it wrong means buying a cuvette that cannot reach the wavelength you need to measure.
JGS1 — synthetic, high-OH
170–2,200 nm · High OH (≈1000 ppm) · Best for deep UV (185–250 nm). The default grade for UV-Vis cuvettes. Equivalent: Heraeus Suprasil 1, Corning HPFS 7980. Use for protein, DNA, sunscreen UV-C work.
JGS2 — natural fused
220–2,500 nm · Standard fused quartz · No useful deep-UV transmission. The cheap “general quartz” used in catalog cells. MachinedQuartz does not stock JGS2 — JGS1 covers the same range plus deep UV at our scale.
JGS3 — synthetic, low-OH
220–3,500 nm · Low OH (<1 ppm) · Best for NIR and IR work. The OH band at 2,730 nm that limits JGS1 is gone. Used for FTIR sample cells, NIR cuvettes, dye-laser windows. Equivalent: Heraeus Suprasil 300, Corning HPFS 8655.
For a deeper breakdown including transmission curves and side-by-side cuvette selection logic, see our Cuvette Material Guide for UV-Vis.
UV-Vis-NIR transmission curve
Fused quartz transmission (10 mm path, with Fresnel losses) breaks down by spectral region as follows:
| Region | Wavelength | Typical Transmission | Notes |
|---|---|---|---|
| Vacuum UV | < 170 nm | 0% | Atmospheric O₂ also absorbs — vacuum required |
| Deep UV | 170 – 220 nm | 50% → 90% (JGS1 only) | JGS2/JGS3 cut off near 220 nm |
| Mid UV | 220 – 280 nm | ~90% | UV-C disinfection, DNA absorbance peak (260 nm) |
| Near UV / Vis | 280 – 780 nm | ~93% | Reflects Fresnel losses, not absorption |
| NIR | 780 – 2,200 nm | ~93% | Drops near 2,730 nm OH band in JGS1; no drop in JGS3 |
| Mid IR | 2,200 – 3,500 nm | JGS3: ~90% · JGS1: 50% | JGS3 required for clean FTIR work |
| Beyond 5 µm | — | 0% | Use CaF₂, BaF₂, or sapphire instead |
The Fresnel reflection loss accounts for the ~7% transmission deficit even at the brightest wavelengths — light is being reflected at the air-quartz interfaces, not absorbed. AR coatings can recover this, but most lab cuvettes are uncoated and accept the loss.
Where quartz is used
Fused quartz is the material of choice across many high-tech and laboratory industries because of its unique combination of UV transparency, thermal stability, chemical inertness, and electrical insulation:
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Spectroscopy
UV-Vis, fluorescence, NIR, Raman cuvettes — the primary commercial market for fused quartz
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Semiconductor
Wafer carriers, diffusion tubes, photomask blanks, EUV pellicle frames
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Lighting
Mercury, xenon, halogen, UV-curing lamp envelopes; quartz heaters
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Lasers
Windows and substrates for 193 nm DUV, 248 nm KrF excimer, high-power Nd:YAG
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Fiber Optics
Preforms for single-mode and multimode telecom fiber drawing
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Labware
Crucibles, evaporating dishes, combustion boats, high-T tube furnaces
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Metrology
Interferometer flats, laser gyroscope blocks, satellite optics
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Optics
Windows, lenses, prisms, mirror substrates for UV through IR
If you are evaluating fused quartz for a specific application, browse our cuvette catalog or send a custom drawing to our custom fabrication team.
Quartz vs glass — what is different
This is the most common source of confusion in lab procurement: a “glass” cuvette and a “quartz” cuvette look identical, but they are not interchangeable for spectroscopy. Here is the short version:
| Spec | Fused Quartz | Borosilicate Glass (Pyrex) | Soda-Lime Glass |
|---|---|---|---|
| Composition | 99.99%+ SiO₂ | SiO₂ + B₂O₃ + Na₂O | SiO₂ + Na₂O + CaO + MgO |
| UV cutoff | 170 nm | 320 nm | 340 nm |
| Max temperature | 1,100 °C | 500 °C | 120 °C |
| Thermal expansion (10⁻⁶/K) | 0.55 | 3.3 | 9.0 |
| Cost ratio | 10x | 1x | 0.1x |
| Use for UV-Vis cuvettes | ✅ Required below 320 nm | ⚠️ Vis only | ❌ Not used |
For a complete decision flowchart, see How to Tell Glass from Quartz and Quartz vs Glass Cuvette.
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Browse Quartz CuvettesFrequently asked questions
Is quartz a mineral or a glass?
Both forms exist. Natural quartz mined from rock is a crystalline mineral with a trigonal structure. Fused quartz — what cuvettes and optics are made from — is an amorphous (glassy) form of the same SiO₂ chemistry, produced by melting natural quartz above 2,000 °C. In optics, “quartz” almost always means fused quartz.
What is the difference between fused quartz and fused silica?
They are chemically identical (both are amorphous SiO₂), but distinguished by purity and manufacturing route. Fused quartz is melted from natural crystalline quartz (typically 99.99% pure). Fused silica is synthesized from gaseous SiCl₄ via flame hydrolysis (99.9999%+ pure). For most applications they are interchangeable; for deep-UV optics and 193 nm laser systems, synthetic fused silica is required. See our Fused Silica vs Fused Quartz guide for the full breakdown.
Why use quartz instead of glass for UV-Vis cuvettes?
Borosilicate and soda-lime glass cut off transmission below 320 nm. Quartz transmits down to 170 nm. If you are measuring proteins (peak at 280 nm), DNA (260 nm), sunscreen UV-C, or any wavelength below 320 nm, you must use a quartz cuvette — a glass cuvette will simply read 0% transmission and the measurement is invalid. For visible-only colorimetry above 320 nm, glass works fine.
Can quartz be scratched?
Yes — quartz is hard (Mohs 5.3–6.5 for fused, 7 for crystalline) but not unscratchable. Diamond (Mohs 10), corundum/sapphire (9), and topaz (8) will scratch it. In normal lab handling with plastic-tipped tweezers and lens tissue, quartz cuvettes last for years. Never use steel forceps or abrasive cleaners on optical surfaces.
What temperature can quartz withstand?
Continuous service temperature for fused quartz is 1,100 °C; short excursions to 1,200 °C are acceptable. The annealing point is 1,180 °C and softening point is 1,683 °C. Above 1,200 °C, gradual crystallization (devitrification) occurs, especially in the presence of alkali contamination. For sustained use above 1,100 °C, consider sapphire or polycrystalline alumina. Thermal shock is generally not a failure mode for quartz — it can be plunged from red heat into ice water without cracking.
Why do my quartz cuvettes always show 7% loss even with no sample?
That is Fresnel reflection loss, not absorption. Light reflects at each air-quartz interface: about 3.5% per surface × 2 surfaces = ~7%. The spectrophotometer’s baseline blank should subtract this away during the auto-zero step. If you are seeing extra loss, check that you are blanking against an identical cuvette with the same solvent — matched-pair sets exist specifically for this.
Is quartz electrically conductive?
No. Pure fused quartz is one of the best electrical insulators known, with dielectric strength of 250–400 kV/cm and resistivity above 10¹⁸ Ω·cm at room temperature. This is why it is used for vacuum tube envelopes, semiconductor processing chambers, and high-voltage insulators. Surface contamination can introduce minor leakage paths, which is why clean handling matters in semiconductor applications.
What dissolves quartz?
Hydrofluoric acid (HF) — readily, even at room temperature — and hot concentrated phosphoric acid above 300 °C. Molten sodium hydroxide and potassium hydroxide also dissolve quartz at high temperatures. Common acids (HCl, H₂SO₄, HNO₃, HClO₄) and almost all organic solvents do not attack quartz, even at their boiling points. This is the basis for using quartz crucibles in trace metal analysis: the acids leach contaminants out of the sample without dissolving the vessel.
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