The group
Every quartz has the same chemistry and the same hardness. What separates a two-dollar tumbled stone from a two-hundred-dollar amethyst is colour, clarity and crystal size — and in the chalcedonies, pattern.
The crystalline half grows as visible single crystals and is cut faceted: amethyst, citrine, ametrine, rock crystal, smoky quartz, rose quartz. Colour here comes from trace iron or aluminium acting with natural irradiation, which is also why several of these colours can be created or destroyed with heat and a radiation source. Most citrine on the market is heated amethyst, and most smoky quartz has been irradiated.
The cryptocrystalline half grows as a mass of microscopic fibres filling a cavity, and is cut as cabochons, slabs and objects rather than faceted. Agate, carnelian, chrysoprase, bloodstone, onyx and the jaspers all belong here. Dyeing is endemic in this half of the family and has been industrial practice since the nineteenth century.
At 7 on the Mohs scale quartz is exactly as hard as the airborne dust that scratches everything else, which is why it wears well and why it is the benchmark the whole scale is built around.
Every quartz compared
The whole group side by side. Where the constants overlap, the species cannot be named from a refractometer alone — which is exactly why the trade names mislead.
| Variety | Species | Colour | Mohs | RI | SG | Guide price |
|---|---|---|---|---|---|---|
| Agate | Chalcedony | colourless | 6.5–7 | 1.530–1.540 | 2.58–2.64 | $0.50–20/ct |
| Agatised Dinosaur Bone | Chalcedony/quartz replacing fossil bone | red | 6.5–7 | 1.530–1.543 (spot ~1.54) | 2.50–2.70 | $1–30/ct for sharply cellular red-and-black material |
| Agatized Coral | Oligocene-Miocene scleractinian coral colonies in which the aragonite skeleton has been replaced by chalcedony - a fossil, and silica, not carbonate | colourless | 6.5-7 | 1.53-1.54 (spot) | 2.55-2.65 | $1-15 per carat cut; display slabs and heads $30-400 each |
| Agatized Dinosaur Bone | Fossil dinosaur bone in which the marrow cavities have been filled with agate, chalcedony or jasper while the bone cell walls are preserved | red | 6-7 | 1.53-1.54 (spot) | 2.5-3.0 (higher where uranium and iron minerals are present) | $5-50 per gram for fine red-and-black cellular material; cabochons $50-1,500; large slabs higher |
| Amethyst | Quartz | violet | 7 | 1.544–1.553 | 2.65 | $5–60/ct |
| Ametrine | Quartz | violet | 7 | 1.544–1.553 | 2.65 | $10–80/ct |
| Aqua Aura | Coated quartz | blue | 7 substrate; the film is far softer | 1.544–1.553 substrate | 2.65 | Clusters 10–200 USD depending on size |
| Aquaprase | Chalcedony | teal | 6.5–7 | 1.530–1.539 | 2.58–2.64 | $10–120/ct |
| Aventurine | Quartzite | green | 6.5–7 | 1.544–1.553 | 2.64–2.69 | $1–15/ct |
| Aventurine Quartzite | Quartzite - a metamorphosed sandstone - containing reflective platy mineral inclusions that give aventurescence | green | 6.5-7 | 1.544-1.553 (1.55 spot) | 2.64-2.69 | $1-8 per kilogram rough; cabochons $2-20; carved bowls and figures $10-200 |
| Biggs Jasper | Jasper (silicified volcanic ash) | yellow | 6.5–7 | 1.53–1.54 (spot) | 2.55–2.70 | Rough 60–300 USD/kg; scenic cabochons 40–250 USD |
| Binghamite | Chalcedony with goethite and hematite fibres | yellow | 6.5–7 | 1.530–1.543 | 2.55–2.70 | Cabochons 30–200 USD; rough scarce |
| Bloodstone | Chalcedony | green | 6.5–7 | 1.530–1.540 | 2.58–2.64 | $0.50–8/ct |
| Blue Lace Agate | Chalcedony (banded) | blue | 6.5–7 | 1.530–1.539 | 2.58–2.64 | $1–15/ct |
| Botswana Agate | Chalcedony (agate) | pink | 6.5–7 | 1.530–1.539 | 2.58–2.64 | Rough 10–50 USD/kg; cabochons 10–50 USD |
| Bruneau Jasper | Jasper (silicified rhyolite) | red | 6.5–7 | 1.53–1.54 (spot) | 2.55–2.70 | Old-stock rough 80–400 USD/kg; cabochons 40–250 USD |
| Bumblebee Stone | Banded volcanic sediment of calcite, gypsum, sulphur, realgar and orpiment from a fumarolic setting - not a jasper and containing no chalcedony | yellow | 3-5 (soft and variable) | 1.49-1.66 approx., mixed | 2.4-2.9 | $20-120 per kilogram rough; cabochons $20-150 |
| Carnelian | Chalcedony | orange | 6.5–7 | 1.530–1.540 | 2.58–2.64 | $0.50–10/ct |
| Chalcedony | Chalcedony | teal | 6.5–7 | 1.530–1.540 | 2.58–2.64 | $1–25/ct |
| Chrysoprase | Chalcedony | green | 6.5–7 | 1.530–1.540 | 2.58–2.64 | $2–60/ct |
| Citrine | Quartz | yellow | 7 | 1.544–1.553 | 2.65 | $5–40/ct |
| Crazy Lace Agate | Chalcedony (agate) | orange | 6.5–7 | 1.530–1.539 | 2.58–2.64 | Rough 5–30 USD/kg; good cabochons 15–80 USD |
| Dalmatian Stone | Quartz-feldspar porphyry - a fine-grained igneous rock with dark phenocrysts; not a jasper and not chalcedony | colourless | 6-7 | 1.54 approx. (spot) | 2.60-2.75 | $2-6 per kilogram rough; bead strands $3-15 |
| Dendritic Agate | Chalcedony | colourless | 6.5–7 | 1.530–1.539 | 2.58–2.64 | $0.50–15/ct |
| Dumortierite Quartz | Quartz with dumortierite inclusions | blue | 7 | 1.544–1.553 | 2.64–2.71 | $1–15/ct |
| Enhydro Agate | Chalcedony (agate) | colourless | 6.5–7 | 1.530–1.539 | 2.55–2.64 | 20–300 USD per nodule depending on how visible the bubble is |
| Fairburn Agate | Chalcedony (agate) | red | 6.5–7 | 1.530–1.539 | 2.58–2.64 | Small field-collected stones 30–300 USD; exhibition-quality pieces in the thousands |
| Feldspar (Industrial) | Alkali and plagioclase feldspars used as a flux to lower melting temperature in glass and ceramics - the single largest industrial use of any silicate after quartz | colourless | 6-6.5 | 1.518-1.539 | 2.55-2.76 | $50-150 per tonne for standard glass and ceramic grades; low-iron and fine-milled grades $180-400 per tonne |
| Fire Agate | Chalcedony | orange | 6.5–7 | 1.530–1.539 | 2.58–2.64 | $20–300/ct for strong multicolour fire |
| Flint | Chalcedony (microcrystalline quartz) | black | 6.5–7 | 1.530–1.539 | 2.57–2.64 | Nominal; priced as rough or as worked artefact |
| Gem Silica | Chalcedony with chrysocolla inclusions | teal | 6.5–7 | 1.530–1.543 | 2.55–2.70 | $20–200/ct for fine translucent material |
| Gneiss | High-grade metamorphic rock with a banded segregation of light feldspar-quartz and dark mica-amphibole layers | colourless | 6-7 | Opaque | 2.65-2.85 | $40-250 per square foot installed; exotic Brazilian gneiss at the top end |
| Granite | Coarse-grained felsic intrusive igneous rock of quartz, alkali feldspar and plagioclase; in the stone trade the word also covers gabbro, anorthosite, gneiss and charnockite | pink | 6-7 (quartz-controlled) | Opaque | 2.60-2.80 | $30-150 per square foot installed; exotic Brazilian and Indian stones $100-400 per square foot |
| Hawk's Eye | Quartz (silicified crocidolite) | blue | 6.5–7 | 1.544–1.553 (spot ~1.54) | 2.64–2.71 | $0.30–6/ct |
| High-Purity Quartz | Quartz refined to extreme chemical purity, used for the crucibles in which silicon is melted for semiconductors and solar wafers - a genuine strategic material | colourless | 7 | 1.544-1.553 | 2.65 | $5-15 per kilogram for standard high-purity grades; $50-300 per kilogram for the highest crucible and optical grades |
| Imperial Jasper | Jasper (orbicular, silicified volcanic) | green | 6.5–7 | 1.53–1.54 (spot) | 2.55–2.70 | Rough 40–250 USD/kg; cabochons 25–200 USD |
| Industrial Silica Sand | Well-sorted, well-rounded, high-purity quartz sand, graded for glassmaking, foundry moulding and hydraulic-fracturing proppant | colourless | 7 | 1.544-1.553 | 2.65 | $15-60 per tonne at the mine for frac and foundry sand; high-purity glass sand $40-120 per tonne |
| Iris Agate | Chalcedony (agate) | colourless | 6.5–7 | 1.530–1.539 | 2.58–2.64 | Thin slices 20–200 USD depending on how strong the diffraction is |
| Irnimite | Jasper with Ba-Mn silicate veins | blue | 6–7 | 1.53–1.55 (spot) | 2.6–2.9 | Cabochons 25–150 USD |
| Itacolumite | A porous quartzite or micaceous sandstone whose interlocking grains have enough space to hinge, so thin slabs genuinely bend | colourless | 6-7 | 1.544-1.553 | 2.30-2.65 (low, because of porosity) | $20-150 per demonstration slab depending on size and how well it flexes |
| Jasper | Chalcedony (opaque) | red | 6.5–7 | 1.530–1.540 | 2.58–2.91 | $0.20–8/ct |
| Laguna Agate | Chalcedony (agate) | red | 6.5–7 | 1.530–1.539 | 2.58–2.64 | Fine rough 100–600 USD/kg; top display faces well into the thousands |
| Lake Superior Agate | Chalcedony (agate) | red | 6.5–7 | 1.530–1.539 | 2.58–2.64 | Tumbled stones 2–20 USD; fine banded specimens 50–500 USD |
| Leopard Skin Jasper | Orbicular rhyolite with spherulitic rings in a fine volcanic groundmass - again a rhyolite rather than a true jasper | pink | 6.5-7 | 1.54 (spot) | 2.55-2.70 | $2-8 per kilogram rough; bead strands $3-20; cabochons $5-30 |
| Lodolite | Quartz with chlorite/clay inclusions | green | 7 | 1.544–1.553 | 2.65 | $1–25/ct |
| Merlinite | Chalcedony or common opal with manganese oxide dendrites | black | 6–7 | 1.48–1.54 (variable) | 2.2–2.6 | Cabochons 10–60 USD |
| Mexican Onyx | Calcite (banded travertine) | colourless | 3 | 1.486–1.658 (spot ~1.49–1.66) | 2.69–2.71 | Carvings and bookends $10–$200; large architectural slabs by the square metre |
| Milky Quartz | Quartz | colourless | 7 | 1.544–1.553 | 2.65 | $0.10–2/g rough |
| Mohawkite | Domeykite and algodonite with native copper in quartz | yellow | 3–3.5 in the metallic phases | Opaque | 3.5–6.0 depending on metal content | Cabochons 25–120 USD; specimens 30–300 USD |
| Mookaite | Chalcedony / radiolarite | red | 6.5–7 | 1.530–1.539 (spot ~1.54) | 2.50–2.70 | $0.20–4/ct |
| Morion | Quartz (variety) | black | 7 | 1.544–1.553 | 2.65 | Faceted stones 3–30 USD/ct; fine natural crystal groups far more |
| Moss Agate | Chalcedony | green | 6.5–7 | 1.530–1.539 | 2.58–2.64 | $0.50–15/ct |
| Mtorolite | Chalcedony | green | 6.5–7 | 1.530–1.539 | 2.58–2.64 | $3–40/ct |
| Myrickite | Chalcedony or common opal with cinnabar | red | 5–7 | 1.45–1.54 (variable) | 2.2–2.7 | Cabochons 20–100 USD |
| Nebula Stone | An unusual alkaline igneous rock of quartz, aegirine, riebeckite and anorthoclase with green orbs in a black ground; a registered trade name from a single deposit | green | 6-7 | 1.54 approx. (spot) | 2.65-2.85 | $30-150 per kilogram rough; cabochons $25-200 |
| Novaculite | Microcrystalline quartz | colourless | 7 | 1.544–1.553 | 2.5–2.6 | $30–400/stone |
| Ocean Jasper | Chalcedony (orbicular) | green | 6.5–7 | 1.530–1.539 | 2.55–2.70 | $0.50–8/ct |
| Onyx | Chalcedony (banded) / calcite (architectural) | orange | 6.5–7 or 3–4 | 1.530–1.540 or 1.486–1.658 | 2.58–2.64 or 2.71 | $0.50–10/ct; slabs $80–600/m² |
| Petrified Wood | Chalcedony / opal replacing wood | red | 6.5–7 | 1.530–1.543 | 2.50–2.70 | $0.20–5/ct; feature slabs by the piece |
| Picture Jasper | Chalcedony / silicified sediment | yellow | 6.5–7 | 1.530–1.539 | 2.55–2.75 | $0.30–6/ct |
| Pietersite | Quartz (brecciated silicified amphibole) | blue | 6.5–7 | 1.544–1.553 (spot ~1.54) | 2.64–2.78 | $1–15/ct |
| Plasma | Chalcedony | green | 6.5–7 | 1.530–1.539 | 2.58–2.64 | Cabochons 10–50 USD; antique intaglios far more |
| Plume Agate | Chalcedony (agate) | red | 6.5–7 | 1.530–1.539 | 2.58–2.64 | Rough 30–200 USD/kg; well-oriented cabochons 40–300 USD |
| Poppy Jasper | Brecciated and orbicular silicified volcanic rock with red and yellow orbs in a darker ground | red | 6.5-7 | 1.53-1.54 (spot) | 2.55-2.70 | $5-40 per kilogram rough; genuine old Morgan Hill material $50-250 per kilogram; cabochons $15-150 |
| Prase | Quartz with actinolite inclusions | green | 7 | 1.544–1.553 | 2.65 | $1–10/ct |
| Prasiolite | Quartz | green | 7 | 1.544–1.553 | 2.65 | $5–40/ct |
| Quartz | Quartz | colourless | 7 | 1.544–1.553 | 2.65 | Clean colourless rough is a few USD per kg; fine faceted varietal material runs 2–50 USD/ct |
| Quartz Cat's Eye | Quartz | green | 7 | 1.544–1.553 | 2.65 | $3–40/ct |
| Quartzite | Metamorphic rock (quartz) | colourless | 7 | 1.54 (spot) | 2.60–2.70 | 1–20 USD per kg rough; cabochons typically under 5 USD |
| Rainforest Jasper | Spherulitic rhyolite - a volcanic rock with radial devitrification spherulites - not a jasper | green | 6.5-7 | 1.54 (spot) | 2.50-2.65 | $3-15 per kilogram rough; cabochons $10-60 |
| Rock crystal | Quartz | colourless | 7 | 1.544–1.553 | 2.65 | $1–50/ct |
| Rose quartz | Quartz | pink | 7 | 1.544–1.553 | 2.65 | $1–20/ct |
| Rutilated Quartz | Quartz with rutile inclusions | yellow | 7 | 1.544–1.553 | 2.65 | $3–60/ct depending on needle quality |
| Sandstone | Clastic sedimentary rock of cemented sand-grade grains, dominantly quartz | yellow | 6-7 where silica-cemented; much softer with carbonate or clay cement | 1.544-1.553 (quartz) | 2.20-2.70 | $3-15 per square foot paving; block stone $200-900 per cubic metre |
| Sard | Chalcedony | orange | 6.5–7 | 1.530–1.539 | 2.58–2.64 | $0.50–8/ct |
| Sardonyx | Chalcedony (banded) | orange | 6.5–7 | 1.530–1.539 | 2.58–2.64 | $1–20/ct; carved cameos priced by workmanship |
| Smoky quartz | Quartz | black | 7 | 1.544–1.553 | 2.65 | $2–30/ct |
| Star Rose Quartz | Quartz | pink | 7 | 1.544–1.553 | 2.65 | $2–25/ct |
| Strawberry Quartz | Quartz with lepidocrocite/hematite inclusions | pink | 7 | 1.544–1.553 | 2.65 | $2–30/ct |
| Thunder Egg | Rhyolite nodule with a chalcedony or agate core | red | 6.5–7 core; 6 shell | 1.530–1.539 (core) | 2.4–2.6 | 5–60 USD per sawn pair; exceptional patterns far more |
| Tiger Iron | Banded iron formation (chalcedony + hematite) | black | 6–7 | 1.530–1.539 (silica bands) | 2.80–3.60 | $0.20–4/ct |
| Tiger’s eye | Quartz after crocidolite | yellow | 6.5–7 | 1.534–1.540 | 2.64–2.71 | $1–20/ct |
| Titanium Quartz | Coated quartz | violet | 7 substrate | 1.544–1.553 substrate | 2.65 | Faceted stones 2–20 USD/ct; clusters 15–150 USD |
| Tourmalinated Quartz | Quartz with schorl inclusions | colourless | 7 | 1.544–1.553 | 2.65 | $2–30/ct |
| Turritella Agate | Chalcedony with fossil gastropods | black | 6.5–7 | 1.530–1.539 | 2.55–2.70 | $0.30–5/ct |
| Unakite | Altered granite (epidote + orthoclase + quartz) | green | 6–7 | 1.52–1.77 (variable by phase) | 2.85–3.20 | $0.20–3/ct |
Questions
Is citrine just heated amethyst?
Most of it, yes. Natural citrine exists and is scarce; the majority of what is sold has been produced by heating amethyst, which is permanent and undetectable without laboratory work. It is not fraud when disclosed, and it is very often not disclosed.
What is the difference between agate and jasper?
Both are cryptocrystalline quartz. Agate is translucent and banded; jasper is opaque and coloured by included clay and iron oxide rather than layered growth. Hold a thin edge to light: if it glows through, it is agate.
Is quartz a real gemstone?
Yes — amethyst, citrine and fine agate have been cut as gems for thousands of years. Quartz is abundant, which keeps prices low, but abundance and authenticity are different questions.
Can quartz be worn every day?
Yes. At 7 on the Mohs scale with no cleavage, quartz handles daily wear better than most coloured stones. Keep dyed material out of strong sunlight, as some dyes fade.
Looking for quartz?
Tell us which variety, what size and what it is for. We source it, photograph it and quote it, with the locality named.
Ask about quartz