Is carnelian a quartz?
Carnelian is quartz: red to orange chalcedony, SiO2, hardness 6.5 to 7. Checked against the quartz sheet, 5 of 7 numbers fit; its RI 1.535 to 1.539 does not.
Yes, with a qualification. Carnelian is red to orange chalcedony, which is microcrystalline quartz, SiO2. Against the Handbook quartz sheet, 5 of 7 lines on the gem society’s carnelian panel fit, hardness 6.5 to 7 against 7 among them; its refractive index, 1.535 to 1.539, sits 0.005 to 0.009 below quartz’s 1.544.
In short
- Yes: carnelian is quartz. The International Gem Society carnelian article calls carnelian a variety of chalcedony, yellow-orange to near reddish orange to orangey brown, formula SiO2. The International Gem Society chalcedony article defines chalcedony as any microcrystalline or cryptocrystalline quartz, and the Handbook of Mineralogy quartz sheet lists fine-grained to microcrystalline (“chalcedony”) as a quartz habit. The September 2026 IMA-CNMNC Master List has a quartz row and no carnelian row.
- The quartz-sheet scorecard. Seven lines of IGS’s carnelian panel against the quartz sheet: formula (SiO2, fits), system (hexagonal, fits), hardness (6.5 to 7 against 7, fits), specific gravity (2.58 to 2.64 against 2.59 to 2.63 massive, fits within 0.01), optic sign (uniaxial +, fits), refractive index (1.535 to 1.539 against ω 1.544, does not), birefringence (0.004 against 0.009, does not). 5 of 7.
- Documented failure: the two optical lines. Carnelian’s highest index, 1.539, is below quartz’s lowest, 1.544. IGS’s own chalcedony panel gives 1.540 to 1.553 and birefringence 0.004 to 0.009, so carnelian’s figures sit at or below the edge of the source’s own range for the parent. No source fetched explains the gap; this page does not either. A refractometer reading cannot prove carnelian is quartz on the sheet’s numbers.
- Is carnelian water safe? The quartz sheet prints no solubility and no reaction with water, gives hardness 7 and calls massive quartz tough. That is all the sheet says, and this page adds no care routine. IGS says carnelian’s iron colour can be darkened by heat, even the sun’s, and that any carnelian should be assumed heated unless you are told otherwise.
- Agate is a separate question. Whether a banded carnelian is also an agate is answered on is carnelian an agate, and the general case for chalcedony on is chalcedony quartz; neither page’s tests are repeated here.
| Line | Carnelian (IGS panel) | Quartz (Handbook sheet) | Chalcedony (IGS panel) | Fits quartz? |
|---|---|---|---|---|
| Formula | SiO2 | SiO2 | SiO2 | Yes |
| Crystal system | Hexagonal (trigonal), microcrystalline | Hexagonal; fine-grained to microcrystalline (“chalcedony”) | Hexagonal (trigonal), microcrystalline | Yes |
| Hardness | 6.5 to 7 | 7 | 7 | Yes |
| Specific gravity | 2.58 to 2.64 (12.25 to 12.42 g in water) | 2.65 (12.45 g); 2.59 to 2.63 massive (12.28 to 12.40 g) | 2.55 to 2.91 | Yes, within 0.01 of the massive range |
| Optic sign | Uniaxial (+) | Uniaxial (+) | Uniaxial (+) | Yes |
| Refractive index | 1.535 to 1.539 | ω 1.544, ε 1.553 | 1.540 to 1.553 | No: 0.005 to 0.009 below ω |
| Birefringence | 0.004 | 0.009 (1.553 − 1.544) | 0.004 to 0.009 | No |
| Score | — | — | — | 5 of 7 |
Is carnelian a type of quartz?
Yes, through chalcedony. The International Gem Society’s carnelian article opens by calling carnelian the best-known variety of chalcedony, ranging from yellow-orange to rich, near reddish orange to orangey brown, and from semi-opaque to highly translucent. Its panel gives the formula SiO2 and records carnelian as a variety of chalcedony. The chalcedony article defines chalcedony as any form of microcrystalline or cryptocrystalline quartz, quartz whose crystals are too small to be seen without high magnification, and records chalcedony as a variety of quartz.
The species is quartz. A whole-word scan of the September 2026 IMA list finds no line containing carnelian or cornelian; quartz has a row, SiO2, status A, 1967 s.p. The Handbook of Mineralogy quartz sheet writes fine-grained to microcrystalline (“chalcedony”), massive, among quartz’s habits, with a lustre waxy to dull when massive. So a carnelian label names a colour variety of a texture of one mineral. The clause-by-clause mineral test is on is quartz a mineral; the chalcedony composition, with its share of moganite, is on chalcedony.
Does carnelian match the quartz numbers? The scorecard
Five lines fit. Formula: SiO2 on both. System: hexagonal on both, IGS adding microcrystalline. Hardness: IGS 6.5 to 7, the sheet 7. Specific gravity: IGS 2.58 to 2.64; the sheet 2.65 for crystals and 2.59 to 2.63 when massive, so carnelian’s range overhangs the massive range by 0.01 at each end. A 20.00 g carnelian reads 12.25 to 12.42 g in water, against 12.28 to 12.40 g for massive quartz. Optic sign: uniaxial (+) on both.
Two do not. IGS gives carnelian a refractive index of 1.535 to 1.539 and birefringence 0.004. The quartz sheet gives ω 1.544 and ε 1.553, a birefringence of 0.009. Carnelian’s whole range lies below quartz’s lower index. IGS’s chalcedony panel, 1.540 to 1.553 with birefringence 0.004 to 0.009, starts 0.001 above carnelian’s top. None of the three sources says how its figures were measured, and no source fetched for this page says why they differ. The refractive index is therefore not evidence for or against carnelian being quartz.
What the scorecard decides. Composition, system, hardness, density and optic sign all point to quartz; on these sources the optical mismatch is unexplained, and the identification rests on the other five lines and the definitions. Density is measured as on how to measure specific gravity at home.
Is carnelian water safe? What the quartz sheet says
The sheet is silent on water. The Handbook quartz sheet has no solubility line and records no reaction with water. It gives hardness 7, variable by direction and form, brittle tenacity, tough when massive, and conchoidal fracture. Carnelian’s IGS panel adds hardness 6.5 to 7 and no cleavage. Nothing in these sources says water harms carnelian, and nothing says it was tested; this page gives no soaking, cleansing or care routine.
What IGS does say. Iron is the source of carnelian’s colour, it can easily be heat treated, even by the sun’s heat alone, to darken red tones as the iron is oxidized, and any carnelian should be assumed enhanced in this way unless you are told otherwise. The chalcedony article says chalcedonies are relatively porous and that dyeing is common. This page gives no test for heating or dye; dye checks are on how to tell if a crystal is dyed.
Is carnelian a gemstone, and where is it from?
A gem variety of a common mineral. IGS treats carnelian as a gem and calls it the best-known variety of chalcedony. It says most commercial carnelian comes from India, with gem-quality sources in Brazil, Egypt and Uruguay; its chalcedony article lists the same four for carnelian. These are IGS statements; the Handbook quartz sheet does not mention carnelian and lists quartz localities generally.
The names around it. IGS calls sard similar to carnelian with a brownish tone, and says a red-based stone with a white upper layer is cornelian or carnelian onyx, a sardonyx. Agate is the separate question on is carnelian an agate; onyx has its own page. The species page is quartz, and more guides are under the collecting guides. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.