Key properties
| Chemical formula | SiO2 |
| Crystal system | Trigonal |
| Mohs hardness | 6.5-7 |
| Toughness | Good |
| Refractive index | 1.530-1.539 |
| Birefringence | 0.0000-0.0040 |
| Optic character | Aggregate (AGG) |
| Specific gravity | 2.55-2.70 |
| Cleavage | None |
| Fracture | Conchoidal to granular |
| Habit | Botryoidal, stalactitic and massive crusts filling vesicles and seams in volcanic rocks; also veins and fossil replacements |
| Lustre | Waxy to dull; polish: Vitreous to greasy |
| UV fluorescence | Usually inert; some bodytypes fluoresce weak yellowish green in long-wave and short-wave UV |
| Pleochroism | None |
| Cause of colour | Trace impurities and pigmenting inclusions rather than lattice chromophores: iron compounds for red, orange, brown and yellow tones, nickel-rich clay (kerolite) for the green of chrysoprase, and disseminated chrysocolla for blue-green gem silica |
| Typical inclusions | Often remarkably homogeneous under magnification • dendrites and moss-like chlorite or hornblende in moss agate • iron-oxide specks and banding in agates • visible structure only at high magnification or in banded material |
| Stability | Stable to light • heat may lighten or shift body colour • hydrofluoric acid attacks it • dyes in treated material can bleach or react with acids |
| Heat sensitivity | Moderate - bench torches and prolonged heating can change colour; dyed material can fade or burn |
| Care and cleaning | Warm soapy water is safe • ultrasonic and steam usually safe for solid untreated material • avoid for dyed or heavily fractured pieces • keep away from strong acids and household chemicals |
| Birthstones | Bloodstone is a March alternate • sardonyx is an August alternate • agate, onyx, carnelian and jasper are traditional zodiac stones (May, July, Virgo and Leo associations) |
| Availability | Most varieties are plentiful and inexpensive; chrysoprase, fine natural blue, gem silica and iris or fire agate are limited to scarce |
| Recognition | Spot RI about 1.53-1.54, SG near 2.60, waxy lustre and an aggregate reaction on the polariscope; the waxy surface and even translucency separate it from crystalline quartz at a glance |
Varieties (8)
Red Chalcedony (Carnelian/Sard)
| Colour | yellowish orange to orangy red and brownish red; sard runs darker and browner |
| Transparency | translucent |
| Clarity type | Translucent ornamental material; clarity grading does not apply |
| Phenomena | None |
| Appearance | Even, glowing orange-red to brick red translucency, usually free of visible inclusions; sard is its darker, less saturated brownish-red counterpart |
| Trade names | Carnelian (cornelian) • Sard (darker brownish red) • Sardonyx (banded sard and white onyx) |
| Misnomers | Red agate for dyed banded material sold as carnelian |
| Typical sizes | Large; beads, tablets and cabochons over 10 ct are routine |
| Cutting styles | Beads • cabochons • cameos and intaglios • carvings • tumbled stones |
| Key separations | Vs red coral: coral shows parallel structural lines and effervesces in dilute acid, chalcedony does not • Vs red glass: bubbles and mould seams in glass, RI variable • Vs jasper: jasper is the granular, opaque member of the same quartz family • Vs dyed red chalcedony: dye concentrates in surface cracks and pits |
| Sources (localities) | Brazil • Uruguay • India • Madagascar |
| Availability | Plentiful and inexpensive |
| Market notes | Steady demand for beads and men's accessories; bright uniform red is usually heat-enhanced, which is accepted trade practice and rarely disclosed |
| Care notes | Warm soapy water safe; ultrasonic generally safe; avoid strong heat which can darken or lighten the colour |
| In short | Carnelian and sard are the iron-stained reds of the chalcedony family, warm and translucent with a waxy glow. Most market material is heated brown chalcedony, a stable and accepted treatment. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–20.00 | $1.00 – $10.00 | commercial | 2026-10-26 |
| 20.00–100.00 | $0.50 – $5.00 | commercial large | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Blue Chalcedony
| Colour | pale sky blue to lilac-grey blue, sometimes with soft banding |
| Transparency | translucent |
| Clarity type | Translucent ornamental material |
| Phenomena | None |
| Appearance | Soft, even sky-blue translucency with a glowing waxy surface; fine material has a delicate, slightly greyish blue that never looks artificial |
| Trade names | Namibian blue chalcedony • Ellensburg Blue (Washington State, USA) • blue chalcedony from the Ray mine, Arizona |
| Misnomers | Dyed blue chalcedony sold as natural blue • milky dyed blue sold as 'moonstone' substitute |
| Typical sizes | Cabochons from a few carats to large 30 ct plus pieces; beads common |
| Cutting styles | Cabochons • beads • carvings |
| Key separations | Vs chrysocolla-included gem silica: gem silica is more blue-green and copper-bearing, chalcedony blue is lighter and greyer • Vs dyed blue chalcedony: dye concentrates in cracks, colour too saturated and even • Vs larimar: larimar RI about 1.60, SG about 2.85, with white marbling • Vs blue glass: bubbles, mould seams |
| Sources (localities) | Namibia (finest) • USA (Arizona, Nevada, Washington) • Turkey • Brazil |
| Availability | Fine natural blue is limited; dyed material is common |
| Market notes | Popular for men's beads and designer cabochons; untreated saturated blue commands a strong premium over dyed lookalikes |
| Care notes | Warm soapy water safe; avoid heat and acids; dyed material may fade with prolonged light exposure |
| In short | Natural blue chalcedony is a softly glowing, translucent blue with strong appeal in designer jewellery. Fine Namibian and American material is scarce; much commercial blue is dyed and should be disclosed. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–10.00 | $8.00 – $60.00 | commercial to fine natural | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Green Chalcedony
| Colour | soft greyish to yellowish green; plasma dark with pale spots, prase leek-green, moss agate colourless with green dendrites |
| Transparency | translucent |
| Clarity type | Translucent ornamental material |
| Phenomena | None (moss-like patterns are inclusions, not a true phenomenon) |
| Appearance | Even leek-green or greyish-green translucency (prase, plasma) or colourless chalcedony carrying green moss-like dendrites (moss agate); never the saturated apple green of chrysoprase unless dyed |
| Trade names | Prase • Plasma • Moss agate (mocha stone) |
| Misnomers | Green onyx for dyed green chalcedony |
| Typical sizes | Large; cabochons and carvings over 20 ct common |
| Cutting styles | Cabochons • beads • carvings • cameos |
| Key separations | Vs chrysoprase: chrysoprase is nickel-coloured with a distinctive apple to leek green translucency, no dye features • Vs dyed green chalcedony: dye concentrates in cracks, pink-red under Chelsea filter, vague absorption bands near 645 and 670 nm • Vs jadeite and nephrite: jades have higher RI (1.61-1.66) and SG (2.95-3.34) • Vs prasiolite: crystalline quartz shows true birefringence |
| Sources (localities) | India and USA (moss agate) • Germany and China (plasma) • Australia and USA (prase-type material) |
| Availability | Natural greens limited; moss agate plentiful |
| Market notes | Moss agate sells as landscape-patterned designer material; dyed green floods the bead market as 'green onyx' |
| Care notes | Warm soapy water safe; avoid heat and acids |
| In short | Natural green chalcedony comes from mineral inclusions, giving prase, plasma and moss agate their quiet greens. Almost any strong, even green in this family should be suspected of dye until proven otherwise. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–20.00 | $1.00 – $20.00 | commercial | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Yellow-Orange Chalcedony
| Colour | honey yellow to golden orange, sometimes faintly banded |
| Transparency | translucent |
| Clarity type | Translucent ornamental material |
| Phenomena | Iridescence in some banded iris agates |
| Appearance | Warm honey to amber-orange translucency, even and glowing, often cut as large clean cabochons or beads |
| Trade names | Honey chalcedony • golden chalcedony |
| Misnomers | Sold loosely as 'citrine' in bead form; citrine is crystalline quartz |
| Typical sizes | Large pieces common |
| Cutting styles | Cabochons • beads • carvings |
| Key separations | Vs citrine: citrine is transparent crystalline quartz with vitreous lustre and true birefringence (RI 1.544-1.553) • Vs hessonite garnet: hessonity is singly refractive with higher RI (about 1.74) and granular roiled look • Vs orange glass: bubbles, mould marks |
| Sources (localities) | Brazil • Uruguay • India • Madagascar |
| Availability | Plentiful |
| Market notes | Steady bead and carving demand; often colour-processed, buy from reliable sources |
| Care notes | Warm soapy water safe; avoid heat |
| In short | Honey-gold chalcedony offers big, clean translucent orange-yellow material at modest cost. Distinguish it from citrine, which is transparent crystalline quartz. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–30.00 | $1.00 – $12.00 | commercial | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
White Chalcedony
| Colour | milky white to very pale grey or cream, often faintly banded |
| Transparency | translucent |
| Clarity type | Translucent ornamental material |
| Phenomena | None |
| Appearance | Even milky-white translucency with a soft waxy glow, frequently used undyed in carved pendants and as the base for dyeing |
| Trade names | Milky chalcedony • white chalcedony |
| Misnomers | Sold as 'moonstone' in cheap jewellery; true moonstone is feldspar with adularescence |
| Typical sizes | Large pieces common |
| Cutting styles | Cabochons • beads • carvings • cameos (white layer of sardonyx) |
| Key separations | Vs moonstone feldspar: moonstone shows adularescence, cleavage, and lower RI near 1.52 with distinct birefringence in transparent material • Vs howlite and magnesite: both take dye strongly; howmite SG about 2.5, dull matte white with grey veins • Vs white jadeite/nephrite: jades have higher RI and SG, denser feel |
| Sources (localities) | Brazil • Uruguay • India • USA |
| Availability | Plentiful |
| Market notes | The base material for most dyed chalcedony products; buy white beads expecting them to be dye candidates |
| Care notes | Warm soapy water safe; porous - avoid dyes and chemicals in wear |
| In short | Milky white chalcedony is the quiet base of the family, used undyed for soft white jewellery and industrially as the canvas for dyed colours. Do not confuse it with moonstone, which is feldspar. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–30.00 | $0.50 – $6.00 | commercial | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Black Chalcedony (Onyx)
| Colour | uniform black, rarely with white banding in sardonyx-style layers |
| Transparency | opaque |
| Clarity type | Opaque ornamental material |
| Phenomena | None |
| Appearance | Sleek uniform black with a bright waxy polish, the classic contrast layer in banded cameos and beads |
| Trade names | Black onyx |
| Misnomers | 'Black onyx' itself is almost always dyed chalcedony • 'black jade' mislabel for dyed chalcedony |
| Typical sizes | Beads and cabochons of all sizes; large flats for cameos |
| Cutting styles | Cabochons • beads • cameos and intaglios • inlay |
| Key separations | Vs obsidian: glass lustre, conchoidal glass fracture, RI about 1.50, bubbles • Vs black glass: bubbles and mould seams • Vs jet: jet SG 1.3, warm to touch, burns • Vs black tourmaline: crystalline, striated prisms, different RI • Vs black nephrite/jadeite: jades higher RI and SG, fibrous or granular texture |
| Sources (localities) | Brazil and Uruguay agate, dyed in processing centres (historically Idar-Oberstein, Germany; today largely Asia) |
| Availability | Plentiful (dyed) |
| Market notes | Uniform black at low cost makes it a staple for contrast inlay, cameos and men's jewellery; natural black chalcedony is a collector curiosity |
| Care notes | Warm soapy water safe; ultrasonic generally safe; avoid acids which can attack the dye, and strong heat |
| In short | Black onyx is almost always dyed chalcedony, delivering uniform sleek black for beads, cameos and inlay. Natural black chalcedony is rare, so uniformity itself hints at treatment. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–30.00 | $0.50 – $8.00 | commercial | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Chrysoprase
| Colour | apple to leek green, light to medium yellowish green, translucent |
| Transparency | translucent |
| Clarity type | Translucent ornamental material |
| Phenomena | None |
| Appearance | Even, glowing apple green translucency unlike any other chalcedony; colour sits in the stone rather than on it, with no dye concentrations |
| Trade names | Australian jade (misleading) • chrysoprase • 'prase' historically for darker green |
| Misnomers | Australian jade (it is not jade) • dyed green chalcedony sold as chrysoprase |
| Typical sizes | Cabochons to large carving rough; clean pieces over 20 ct prized |
| Cutting styles | Cabochons • beads • carvings • inlay |
| Key separations | Vs dyed green chalcedony: dyed material shows colour concentrations in fractures, pink-red under the Chelsea filter and vague absorption bands near 645 and 670 nm; natural chrysoprase shows none of these • Vs jadeite and nephrite: jades have higher RI and SG • Vs prasiolite: crystalline quartz with true birefringence |
| Sources (localities) | Australia (Marlborough, Queensland - world standard) • Poland (Szklary) • Brazil • Tanzania • Kazakhstan • Madagascar |
| Availability | Limited; fine Australian material scarce |
| Market notes | Fashion cycles (it was a favourite of Faberge and again in modern designer jewellery) move prices sharply; buy on evenness and strength of colour |
| Care notes | Warm soapy water safe; avoid ultrasonic on fractured pieces; colour stable to light but avoid strong heat |
| In short | Chrysoprase is the nickel-coloured apple green of the chalcedony family, at its best from Queensland, Australia. Even, translucent, natural green at a fraction of jade's price, it must be separated from ubiquitous dyed imitations. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–10.00 | $5.00 – $40.00 | commercial to fine | 2026-10-26 |
| 10.00–50.00 | $30.00 – $150.00 | fine Australian | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Dyed Green Chalcedony
| Colour | saturated, very even emerald to bottle green unlike natural chalcedony greens |
| Transparency | translucent |
| Clarity type | Translucent ornamental material |
| Phenomena | None |
| Appearance | Overly perfect, uniform saturated green; colour can sit too deep and even compared with the subtle nickel green of chrysoprase |
| Trade names | Green onyx • 'Australian jade' (when mislabelled) • 'lime chalcedony' |
| Misnomers | Green onyx (dyed chalcedony) • mislabelled chrysoprase or jade |
| Typical sizes | Beads and calibrated cabochons of all sizes |
| Cutting styles | Calibrated cabochons • beads • carvings |
| Key separations | Chelsea filter: dyed green often appears red or pinkish • Magnification: colour concentrations in surface cracks, pits and around drill holes • Spectroscope: vague bands near 645 and 670 nm in many dyes • Vs chrysoprase: chrysoprase passes all these tests clean |
| Sources (localities) | Base white chalcedony mainly Brazil and Uruguay; dyed in Asia and Germany processing centres |
| Availability | Plentiful |
| Market notes | Cheap, cheerful and everywhere in the bead trade; perfectly legitimate when sold as dyed |
| Care notes | Warm soapy water only; dyes can bleach with acids, strong light or heat - no ultrasonic for badly dyed pieces |
| In short | Dyed green chalcedony is the bead market's standard green, sold honestly as 'green onyx' when labelled correctly. A Chelsea filter, a loupe and a healthy suspicion of perfect even green separate it from chrysoprase. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–30.00 | $0.50 – $6.00 | commercial | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Sources
GIA gem encyclopedia · mindat.org · Wikipedia
Data compiled and fact-checked against gemmological literature, October 2026 (JDMIS gem reference). Properties are ranges accepted in gemmological practice; individual stones vary.
See also
Gemstone reference entries: gem #30 · gem #58 · gem #94 · gem #95 · gem #96 · gem #141 · gem #186 · gem #211
Related materials: Quartz
Identification wizard · All 83 materials · Singapore gem labs