Cutting quartz
Quartz has a refractive index of 1.544 to 1.553 and a dispersion of 0.013, a specific gravity of 2.66 and a hardness of 7 on the Mohs scale (trigonal crystal system). It is doubly refractive (uniaxial), with a birefringence of 0.009. Its critical angle, from the low end of the range, is 40.4°, so a round design needs a pavilion of at least 40.4° for head-on light to reflect off both sides of the pavilion and leave through the table.
Quartz shares amethyst's species (quartz) and its optical constants in our trace (within 0.001 of refractive index midpoint and the same fire spread), so these are amethyst's figures. So this page ranks the cuts with amethyst's figures, and each cut links its amethyst page. Quartz's own constants are in the table below, with their sources.
Quartz optical properties
Published values, as on the quartz glossary page; they change a little from stone to stone. Where a property has a range, we calculate angles from the lower refractive index. It gives the stricter limit. Sources: GIA · International Gem Society · Gemdat.
The top ten cuts in quartz
In quartz, the Oval Cut performs best of the 23 jewelry cuts we score: 52 for brilliance, 69 for fire and 87 for scintillation. The Teardrop Cut follows at 49, 60 and 81, then the Pear Cut at 52, 60 and 76.
| Cut | Brilliance | Fire | Scintillation |
|---|---|---|---|
| Oval, Jewelry cut | 52 (T73 benchmark 72) | 69 (T73 benchmark 36) | 87 (T73 benchmark 80) |
| Teardrop, Jewelry cut | 49 (T73 benchmark 72) | 60 (T73 benchmark 36) | 81 (T73 benchmark 80) |
| Pear, Jewelry cut | 52 (T73 benchmark 72) | 60 (T73 benchmark 36) | 76 (T73 benchmark 80) |
| Asscher, Jewelry cut | 60 (T73 benchmark 72) | 52 (T73 benchmark 36) | 72 (T73 benchmark 80) |
| Trillion, Jewelry cut | 60 (T73 benchmark 72) | 44 (T73 benchmark 36) | 80 (T73 benchmark 80) |
| Cushion, Jewelry cut | 69 (T73 benchmark 72) | 24 (T73 benchmark 36) | 85 (T73 benchmark 80) |
| Square, Jewelry cut | 65 (T73 benchmark 72) | 34 (T73 benchmark 36) | 78 (T73 benchmark 80) |
| Trilliant, Jewelry cut | 63 (T73 benchmark 72) | 34 (T73 benchmark 36) | 79 (T73 benchmark 80) |
| Emerald Square, Jewelry cut | 61 (T73 benchmark 72) | 40 (T73 benchmark 36) | 72 (T73 benchmark 80) |
| Marquise, Jewelry cut | 38 (T73 benchmark 72) | 48 (T73 benchmark 36) | 86 (T73 benchmark 80) |
In quartz, the DG-M5 Cut performs best of the 11 brilliants we score: 85 for brilliance, 50 for fire and 85 for scintillation. The DG-Anteros Cut follows at 82, 54 and 80, then the DG-Vitruvio Cut at 71, 36 and 98. Of the three, the DG-M5 Cut has the highest brilliance and the DG-Anteros Cut has the most fire.
| Cut | Brilliance | Fire | Scintillation |
|---|---|---|---|
| DG-M5, House cut | 85 (T73 benchmark 72) | 50 (T73 benchmark 36) | 85 (T73 benchmark 80) |
| DG-Anteros, Brilliant | 82 (T73 benchmark 72) | 54 (T73 benchmark 36) | 80 (T73 benchmark 80) |
| DG-Vitruvio, Brilliant | 71 (T73 benchmark 72) | 36 (T73 benchmark 36) | 98 (T73 benchmark 80) |
| DG-Broken Hearts and Arrows, Brilliant | 71 (T73 benchmark 72) | 35 (T73 benchmark 36) | 86 (T73 benchmark 80) |
| T73 Round Brilliant, Benchmark | 72 | 36 | 80 |
| T105 Round Brilliant, Brilliant | 65 (T73 benchmark 72) | 31 (T73 benchmark 36) | 90 (T73 benchmark 80) |
| DG-Miliano, House cut | 60 (T73 benchmark 72) | 28 (T73 benchmark 36) | 98 (T73 benchmark 80) |
| T57 Round Brilliant, Historic cut | 71 (T73 benchmark 72) | 37 (T73 benchmark 36) | 72 (T73 benchmark 80) |
| Old European, Historic cut | 59 (T73 benchmark 72) | 37 (T73 benchmark 36) | 81 (T73 benchmark 80) |
| DG-Rafaello, House cut | 45 (T73 benchmark 72) | 26 (T73 benchmark 36) | 96 (T73 benchmark 80) |
Brilliance is the share of face-up light that the stone returns. Fire is the share of that light that splits into color. Both come from our face-up light census. Scintillation is the sparkle that facets give as a stone moves, and we read it from the facets of each cut. We score 37 cuts, the same figures as our Cut Performance Index. The Cut Performance Wheel does not model this stone yet. Mazarin, Peruzzi and Old Mine, historic cushions, are in neither list. Each measured cut’s own page shows its figures in every gemstone we trace. A simulation of the geometry, not a grading report.
Quartz: questions
What pavilion angle should I use for quartz?
For a round design, at least 40.4°. At that angle or steeper, light that arrives straight down reflects off both sides of the pavilion, beyond the critical angle of quartz (40.4°). Then it leaves through the table. The angle is the larger of the critical angle and (180° − critical angle) / 4. Faceters usually cut a degree or two steeper, for light that arrives off the axis. Fancy shapes vary, so every cut page lists its own figure.
Why does quartz show amethyst's figures?
Quartz shares amethyst's species (quartz) and its optical constants in our trace (within 0.001 of refractive index midpoint and the same fire spread), so these are amethyst's figures. Our alias rule: the same species, a refractive index midpoint within 0.005 and a fire spread within 0.002 of the stone whose figures it takes; quartz is within 0.001 and 0.000.
What is the critical angle of quartz?
40.4°, from a refractive index of 1.544, the low end of its published range. Light that strikes a facet from inside the stone at less than this angle from the normal of the facet passes out. At a larger angle, it reflects.
Which cuts work best in quartz?
We add brilliance, fire and scintillation together. By that total, the DG-M5 Cut, the DG-Anteros Cut and the DG-Vitruvio Cut are the best brilliants in quartz. By the same total, the best jewelry cuts are the Oval Cut, the Teardrop Cut and the Pear Cut. We score 37 cuts in all, and this page ranks the top ten of each.
How much does quartz weigh compared with diamond?
Quartz has a specific gravity of about 2.67, and diamond has 3.52. So a stone of the same size weighs about 0.76 times as much as the diamond.