Agate

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Agate is the banded form of chalcedony, a cryptocrystalline variety of quartz. Rather than a single crystal, it is composed of a myriad of miniature crystals that can only be seen with extreme magnification. Agate's name is derived from the site of its discovery, the river Achates (now Dirillo) in southwest Sicily. You will often find striking curved or angular banded patterns of color flowing within agate, which are caused by the presence of various minerals, often iron and manganese. One of the oldest known gemstones, agate is a favored material of lapidaries and artisans around the world.

Agate Polished
Agate Classification
Common Name Agate
Species Quartz
Agate Optical Properties
Transparency Semitransparent - Translucent
Dispersion Strength: None
Refractive Index 1.535-1.539
Birefringence 0.004
Optic Character NA
Optic Sign NA
Polariscope Reaction Aggregate (AGG)
Fluorescence SWUV: Inert
LWUV: Inert
Pleochroism None
Agate Characteristic Physical Properties
Hardness 6.5-7
Specific Gravity 2.550-2.700 Typical:2.600
Toughness Excellent
Inclusions Typical agate is described as having curved angular banding or layers, but it can also have a plume or moss like appearance. Bands may have a very fine grain or fibrous structure due to its microcrystalline structure and may vary in translucency. Agate is sometimes dyed.
Luster Greasy, Vitreous
Stability Good
Fracture Conchoidal, Granular
Cleavage None
Agate Chemistry & Crystallography
Chemical Name silicon dioxide (aka silica)
Chemical Formula SiO2
Crystal System Trigonal
Chemistry Classification Silicate

Agate Colors

  • Bi-color Agate Bi-color
  • Yellow Agate Yellow
  • White Agate White
  • Red Agate Red
  • Purple Agate Purple
  • Gray Agate Gray
  • Black Agate Black

Countries of Origin

Argentina; Romania; United States of America (the); Uruguay; Madagascar; Kenya; Thailand; India; Mozambique; Morocco; Unknown; Botswana; China; Namibia; Brazil; Italy; Mexico; South Africa; Germany

History

One of the most varied of all gems, agate is a chalcedony that appears in a wide array of colors with a plethora of unique patterns and bands. Agate is composed of a myriad of miniature quartz crystals which can only be seen with extreme magnification. The miniature crystals stack upon one another to create a banded look, with an effect that is reminiscent of velvet fabric. You will often find striking, curved, or angular-banded patterns of color flowing within agate, the result of the presence of various minerals. Agate can be many colors, including pink, brown, white, red, gray, black, or yellow. It is porous and accepts dye beautifully, opening many color options. Crazy lace agate from Mexico can have wild and wonderful patterns; landscape agate boasts bands of horizontal orientation that mimic mother nature's mountains and valleys. Blue-lace agate is known for its soft blue color and lace-like white bands. Dendritic agate boasts fern-like inclusions caused by metallic oxides. There's also moss agate and fire agate. Whether you buy agate in a slice from a large geode or buy something dainty to string around your neckline, agate is sure to please.

Care

Agate is often cut en cabochon and polished to optimize its banding. You will also find wonderful cameos and other carved objects made of banded chalcedony.

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More About Agate

Agate plays an important role in folkloric medicine and was once believed to cure the stings of snakes or scorpions. Some Native American groups revered it as a stone that could strengthen the body and calm the spirit. The ancient Egyptians believed that agate quenched thirst and protected the wearer from lightning. The ancient Chinese gave agate credit for bringing luck and opportunity and for energizing one's chi.There are as many folkloric beliefs touting agate's "powers" as there are patterns to be found in the stones. Whatever you choose to believe, there is one certain thing: agate is a splendid stone!

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Species/Variety

Blue Lace Agate

Blue lace agate comes from the Republic of Namibia and Kenya and is known for its powder blue coloring and white parallel wavy bands that resemble lace.

Blue Lace Agate Agate
Blue Lace Agate Classification
Common Name Blue Lace Agate
Blue Lace Agate Characteristic Physical properties
Inclusions Blue lace agate is a distinctive blue and white alternating banded material.

Picture Agate

Picture agate displays natural inclusions that formed within the stone in such a way as to create well-defined images. These images have a natural, life-like, picturesque appearance and make picture agate a treasured stone among gemstone lapidaries.

Picture Agate Agate
Picture Agate Classification
Common Name Picture Agate
Picture Agate Characteristic Physical properties
Inclusions The picture agate inclusions form a pattern that give the appearance of a landscape or picture.

Optical Phenomena

Iris Agate

A semitransparent to translucent member of the chalcedony species, iris agate is a phenomenal variety exhibiting an iridescent rainbow-like range of colors throughout the stone. It is highly prized by collectors and designers.

Iris Agate Agate
Iris Agate Classification
Common Name Iris Agate
Iris Agate Characteristic Physical properties
Inclusions Iris agate iridescence has a banded appearance.

Fire Agate

Fire Agate is one of those gems whose beauty and appeal is hard to describe with mere words. A phenomenal gem, it is an opaque variety of chalcedony that exhibits a colorful iridescence. The iridescence is caused by layers of silica and iron oxides, which interfere with the passage of light. Diffraction causes the colorful metallic hues that make this gemstone a favorite of collectors. Its brown body color is also a result of the iron oxide content.Gem quality fire agate is by far rarer than diamonds, emeralds or rubies and is as colorful as any precious Australian opal, although it is typically sold at a fraction of the cost.

Fire Agate Agate
Fire Agate Classification
Common Name Fire Agate
Fire Agate Characteristic Physical properties
Inclusions Fire agates iridescent colors and botryoidal growth structure make it distinctive.

Inclusions

Moss Agate

Moss agate is a variety of chalcedony with contrasting white and green moss-like patterns. Its green coloration comes from a mineral called chlorite, while the reds and browns come from manganese oxide or the oxidation of iron hornblende. Moss agate is generally cut into thin slabs and polished to best display its natural patterns. Often moss agate cabochons are used in distinctive jewelry designs.

Moss Agate Agate
Moss Agate Classification
Common Name Moss Agate
Moss Agate Characteristic Physical properties
Inclusions The stone has dendritic, chlorite or hornblende mineral inclusions that have the appearance of moss.

Dendritic Agate

This agate variety is termed "dendritic" due to its internal collection of dendrites. Dendrites are fern-like inclusions of iron, manganese, or other metallic oxides that create bold patterns within the gem. Typically, dendritic agates are cut into slabs to best exhibit nature's artwork. As you might guess, these pieces are one-of-a-kinds, as no two dendritic patterns are exactly the same.

Dendritic Agate Agate
Dendritic Agate Classification
Common Name Dendritic Agate
Dendritic Agate Characteristic Physical properties
Inclusions Dendritic inclusions are green, brown or black iron or manganese and look like branches.
Tim Matthews

Author

Tim Matthews

Tim Matthews is President and Chief Executive Officer of Jewelry Television® (JTV), as well as a member of the company's Board of Directors. He oversees and leads all aspects of the company's powerful omni-digital retail platform that uniquely specializes in fine jewelry and gemstones. His passion for business and gemstones has led him to become a recognized expert in the field of gemology. He is a life member of the Gemmological Association of Great Britain (Gem-A) and has earned Gem-A's highest degrees, the Gemmology (FGA) and Diamond (DGA) diplomas. He is also a Graduate Gemologist (GG) of the Gemological Institute of America (GIA) and has also completed GIA's Graduate Diplomas in Diamonds, Colored Stones and Pearls. Under his leadership, JTV has become the leader in the sourcing and selling of color gemstones and jewelry.

This page was created on June 27, 2014.

This page was last edited on October 24, 2019.