Like agate, onyx is a type of chalcedony, which is a cryptocrystalline quartz. The key difference between the two stones is that the characteristic bands we admire in agates are curved, while those in onyx are straight, usually alternating between black and white or brown and white.

Onyx is a favorite material for cameo makers, who will frequently carve into, say, a white layer until they’ve removed enough of it to reveal the black layer below. In this case, the result is a white image that appears to float on an inky background. Onyx is also cut into beads for necklaces, teardrops or geometric shapes for earrings, and bold cabochons for rings.

Also like agate, onyx is easy to dye. The recipe calls for boiling the stone in a sugar solution, then letting it steep in sulphuric acid. When the acid hits the sugar, black carbon is created, which seeps into the stone. This technique is used a lot because the demand for black onyx far outstrips the supply. In fact, dyed black onyx was used liberally during the Art Deco era, when dramatic contrasts and hard edges were all the rage.

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Estate Jade Onyx Lustrous Seed Pearl Gold Long Drop Dangle Earrings NrModern Sterling Silver Rose Color Gold White Onyx Large Sapphire Ring NrTrue Vintage 1978 14kt Solid Gold/onyx Mens Ring Personally InscribedModern Diamond Onyx Pearl 14k Gold Sterling Silver Flower Pendant Necklace NrAntique Art Deco 10k White Gold Ladies' Ring W/ Onyx & White DiamondFine Victorian Rose Gold Seed Pearl & Onyx Large RingEstate Oval Cut Cabochon Green Onyx 18k Gold Rope Ring Nr$3500! Natural Black Onyx & 10pt Diamond 14k 2 Tone Gold Mens Band Ring 10.5g Estate Antique Victorian 14k Rose Gold Greek Goddess Black Onyx Cameo RareVintage Chinese Solid 14k Gold & Onyx Bar Link Bracelet~finely Engraved DragonsAntique 10k Yellow Gold Black Onyx Intaglio Cameo Cocktail Ring Size 6.5 NrVintage 1955 10k Solid Gold Ft. Smith Arkansas High School Class Ring Black OnyxAntonio Pineda Taxco 970 Silver Vintage Onyx Ring Size 6 Mexico Mexican Signed18kt Gold Green Onyx Chalcedony Sardonyx Carved Lady Fancy Cameo Pearl PendantAntique Estate Gothic Victorian Onyx Mourning Rose 10k Engraved Ring Not ScrapVintage Men's Fraternal Ring 10k Wht Gold S 10.5 Onyx W/ Stone Monogram B As IsSquare Onyx W/diamond Mens Ring 10kFine Celtic Design Diamond & Onyx Large Gold RingVintage Tiffany Paloma Picasso Modernist Sterling Silver Onyx Ring,7 1/4Vintage 9ct Gold Black Onyx Gents Initial I Signet RingVintage 4.5 Grms Scrap/wear 10 Kt Gold Genuine Onyx Diamond Mens Signet M Ring Vintage Mexican Modernist Sterling Silver Black Onyx Inlay Collar NecklaceStunning Art Deco 18k Gold Diamond & Onyx Brooch17. Scarce Antique 14k Gold Filigree Ring Emerald Green Onyx Diamond NrFabulous! Sterling Silver Black Onyx Peridot Modernist Ring Signed Zina! Size 7Vintage Judith Jack Sterling Silver & Marcasite W. Onyx Pin / Brooch & Earrings Antique Victorian Solid 14k Gold Jet Black Onyx Mourning Brooch Pin Circa 1800sElegant Art Deco Sterling Silver Black Onyx Marcasites Brooch Pin Excellent Cond18" 14k Gold Onyx 3 Strand Malachite Lapis Amethyst Necklace Vintage Estate FindVintage Onyx Kitten Cat Heart Sterling Silver 925 Charm PendantEstate Sterling Silver Vintage Ring Lot Scrap Sell Filigree Onyx TopazAntique Sterling Silver Art Deco Geometric Black Onyx & Marcisite Necklace Avi Soffer Sterling Silver Pendant W/black Onyx Stone .925Sterling Marcasite Black Onyx Art Deco Earrings /je113Antique Hard Stone Onyx Cameo Finding Set In 14k. Gold & Seed Pearls "warrior"Vintage Bgm Onyx Sterling Silver 925 Ring 6.75Sterling 925 Vintage Mens Black Onyx Inlay Signed Ps Huge Ring 8 Gram Size 14.5Vintage Sterling Silver - Black Onyx Crescents 10.3g - Hoop Earrings Id730Antique C. 1920s Art Deco Sterling Silver Black Onyx Marcasite Lavalier NecklaceGold On Silver Onyx Crown Ring Huge Fantastic Top QualityLot 4 Vintage Sterling Silver Marcasite, Shell & Black Onyx Bracelets | J BtVintage 12k + Sterling Black Hills Gold Onyx Eagle Band Ring 8.1g Sz 9.75 NrVictorian Antique Estate 10k Gold Onyx Black Mourning Pin Brooch Pendant N/rEstate Sterling Silver Vintage Ring Lot Scrap Sell Onyx Claddagh DolphinAlwaysbelisting: Barse 925 Sterling Silver Black Onyx Cross Pendant - 60035Vintage Sterling Silver - Oval Onyx Inlay 57.8g - Bracelet (7.25") Io928Art Deco Antique Estate 10k White Gold Onyx Black Filigree Openwork Necklace N/rStunning Vintage .925 Sterling Silver Black Onyx Marcasite Poison Box Ring14kt Dated 1902 Heavily Carved Black Onyx Ring Ornate 4.4grs Nr36" 14k Gold Onyx Asian Carved Beaded Necklace Vintage Estate FindVintage Sterling Silver, Onyx & Marcasite Art Deco NecklaceVintage [onyx] Sterling "modernist" Art Deco Detailed Earrings Awesome Est Pc Antique 10k Yellow Gold Black Onyx Ring With Star (frat Or Masonic?) NrOld Pawn Native American Sterling 925 Large Claw Turquoise & Onyx Ring Sz 9.5Old Vintage Sterling Silver Black Onyx Poison Secret Compartment Ring Sz 8.5 6gVtg Art Deco Long 64" Single Strand Flapper Genuine Pearl & Onyx Necklace LovelyLot Vtg Sterling Silver Ring Stacked Taxco Mexico Black Onyx Dome Long ModernistG. Webster Designer Signed Sterling Amethyst Onyx And Opal Earrings Vintage ~nr~Vintage Onyx Turquoise Lapis Coral Sugilite Link Sterling 925 BraceletStunning Antique Fair Find Brooch Elegant Pearls & Black Onyx Vintage Jewellery