Agates are a type of chalcedony, which is a cryptocrystalline quartz. Agates grow in the voids of rock masses such as lavas, building themselves in layers from the outside-in over millions of years. As the softer, surrounding rock erodes away, the agates remain. Sometimes these agates are themselves eroded and smoothed into pebbles in riverbeds. Other times they can be found as solid nodules that can be sliced and policed, or hollow geodes whose interiors are studded with jagged crystals.

The most common types of nodular agates are marked by distinct, concentric bands. The differences in the colors of the bands in a given agate are due to the impurities in the silica, the basic mineral of the forming rock. Dendritic or landscape agates refer to white gemstones whose inclusions, usually iron-based, resemble a tree or bush growing throughout the stone. Landscape agates are usually cut and shaped so that one of these trees is centered within the finished gem.

The inclusions in moss agates are finer still, caused by manganese (to produce blacks and browns) and chloride (shades of mossy green). And when polished, fire agates reveal clusters of mineral bubbles that appear suspended within the iridescent jewel.

Two other types of agates are created when silica replaces organic materials rather than filling rocky voids. Petrified or agatized wood is formed when wood that has been surrounded by sediments and deprived of oxygen, thus preventing its outright decomposition, is replaced by silica that slowly takes its shape. Agatized coral is formed in much the same way, although these stones are far more rare.

The use of agates in jewelry dates to the end of the stone age; neolithic agate beads believed to be 9,000 years old have been found in Anatolia, present-day Turkey. Thought to provide protection from the evil eye, agates are frequently sliced, cut, and polished into cabochons for rings, bracelets, pins, and pendants. The stone is also carved into cameos.

Art Nouveau and Arts and Crafts jewelers favored agates over traditional gemstones like diamonds, rubies, and sapphires because they appeared more naturalistic. That said, because agates are relatively porous, they are routinely dyed to accentuate their natural colors, thus adding even more differentiation and drama to their naturally occurring bands. In principle, jewelers should disclose whether or not an agate has been dyed, but one way to tell is to put a stone in a sealed plastic bag—when it’s hot out, the agate will sweat out some of its dye.


Best of the Web (“Hall of Fame”)

All About Jewels Dictionary

All About Jewels Dictionary

This incredible reference dictionary on jewelry, from Enchantedlearning.com, is both beautiful and comprehensive. S… [read review or visit site]

Morning Glory Antiques and Jewelry

Morning Glory Antiques and Jewelry

Jewelry collectors, feast your eyes on this internet gem! It's a goldmine of jewelry information featuring all styl… [read review or visit site]

Cathy Gordon's Jewelry Gallery

Cathy Gordon's Jewelry Gallery

With its vast galleries featuring clear images of jewelry and style, this site really covers it all! Divided up by … [read review or visit site]



Clubs & Associations

Other Great Reference Sites

Most watched eBay auctions    

Antique Victorian Jewellery Scottish Agate-brooch-beetle-chinese Scrimshaw RingSuperb Large Antique Victorian -1868 - Scottish Agate & Quartz Silver Pin BroochAntique Victorian Scottish Loose Agate-seal-ring-brooch-earrings-bracelet-repairVictorian Scottish Chalcedony Agate, Citrine And Silver Thistle BroochFine Antique Victorian Gold Filled (?) Black Enamel Necklace Agate Cameo PendantSuperb Looking Modernist C1960s Kupittaan Kulta Finland 925 Silver BroochArt Nouveau Scottish Moss Agate And Silver Pendant With Silver ChainEdwardian Scottish Montrose Agate And Silver Bird BroochVintage C1960s Silver Signed Iona John Hart Celtic / Scottish Agate Set RingBeautiful Antique Victorian Scottish Polished Agate Stone Bracelet Bangle (c7)Vintage Jewellery Stunning Large Banded Agate Pendant & '925' Silver ChainAntique Victorian Banded Agate Boot & Shoe Watch Fob / Lucky Charms / Love TokenVintage Signed Miracle Scottish Celtic Knot & Carnelian Agate Plaid Brooch PinAntique Victorian Sterling Silver Set Scottish Agate Plaid Brooch Shawl Kilt PinSterling Silver Watch Chain Fully Hallmarked Victorian 1897 Scottish Agate Fob Vintage Jewellery Fabulous Polished Agate Cabochon NecklaceScarce 1962 Modernist Kupittaan Kulta Turku Elis Kauppi Finland Silver BroochVtg Black Gray Oval Moss Agate Scalloped Etched Sterling Cuff BraceletC 1880 Vintage Signed Jewellery Stunning Amethyst Agate Silver Brooch Lace PinVintage Jewellery Gorgeous Sterling Silver & Banded Agate Pendant NecklaceHeavy Vintage Navajo 1940s Harvey Era Stamped Sterling Ingot Agate Cuff BraceletStunning Old Antique Silver Scottish Agate & Citrine Collar Stud Button (a11)Superb Big Antique Victorian C 1900 Silver Scottish Agate Dirk Kilt Pin Brooch Vintage1950 Sterling Silver Western Bolo Tie AgateVictorian Pin Brooch Gold Filled Agate? Onyx? Turquoise Stone Big 2 3/8 Antique40's Vintage Mexico 925 Sterling Silver Agate Necklace Bracelet Demi Signed SetVintage Amethyst Agate Scottish Thistle Brooch By Miracle (?)Georgian 9ct Gold Fill Pocket Watch Fob Ket Set With Agates No.2.Antique Agate Brooch.Estate Sterling Silver Blue Lapis Lace Agate Chandelier Long Drop Earrings NrSuperb Victorian Scottish Agate And Silver Brooch With Kite Mark Date 1875Superb Large Antique Victorian C1890 Silver Scottish Agate Citrine Brooch PinCollection Of Loose Antique Victorian Agate Seals & Micro Mosaic Plaque (c16)Vtg~old Pawn~native~navajo~sterling~silver~agate~ornate~cuff~braceletVtg Southwestern Gorgeous Tribal 3-stone Agate Bracelet/cuff W/coordinated Ring Superb Vintage Art Deco Circa 1930 Sterling Silver Scottish Moss Agate Bracelet Fine Antique Victorian 9ct Rose Gold Pearl Agate Daisy Cluster Ring Uk N 1/2Vintage Silver Scottish Agate Padlock Charm Bracelet Love Token Victorian Silver Gold Black White Stripe Banded Agate Bead Lucky Charms Pendant Antique Scottish Faceted Carnelian/agate Bead Necklace Victorian, Long String.Rare Tiffany & Co 18k Gold Agate Gemstone Beaded Tassel Lavaliere NecklaceAntique Victorian C 1890 9 Ct Gold Scottish Agate Citrine Ornate Brooch PinSuperb Large Antique Victorian C1890 Sterling Silver Scottish Agate Brooch PinAntique Gilt Metal Engraved Watering Can Charm,inset Agate Wax Letter Sal BaseVintage Navajo Unique Pretty Picture Agate Sterling Silver BraceletAntique Victorian Sterling Silver Scottish Agate Brooch/pinLarge Antique Victorian C1890 Silver Scottish Agate Carnelian Pebble Brooch PinAntique Victorian Scottish Agate Rum Bloodstone & Citrine Silver Brooch Kilt PinUncas Moss Bird Picture Agate Sterling Ring Sz 7 Silver Vintage AntiqueEarly Antique Solid Silver Agate Malachite Brooch/pin Dated 1948Antique Botswana Agate Druzy & Apatite Quartz .925 Silver Jewelry Necklace 18''Antique Victorian Gilt Metal And Banded Agate Bracelet Vintage Jewellery Scottish Celtic Love Knot Pebble Agate Plaid Brooch Kilt PinVintage Hand Knotted Scottish Agate NecklaceVintage Klapmeier Miles City, Montana Moss Agate Sterling Silver Brooch 1920s Art Deco Ostby Barton Green Moss Agate Sterling Filigree Ring Titanic NrVictorian Scottish Montrose Agate And Silver BroochLarge Scottish Agate Brooch / Pin On Slate. For Spares / Repair.Vintage Sterling Silver Beautiful Agate, Jade? Large Slider Pendant~vtg~native~navajo~"sandcast"~sterling~silver & Agate~ornate~design~ring~size 7~