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Agate

Quartz

By Tim Matthews, JD, FGA, GG, DGA,
CEO and President of JTV (retired)
Published: June 2014
Modified: October 2023
Agate Polished Agate Rough Agate Jewelry
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Table of Contents
  • General Information
  • Agate Colors
  • Countries of Origin
  • History
  • Care
  • More About Agate
  • Species/Variety
  • Optical Phenomena
  • Inclusions

Agate is the term used to describe the banded form of chalcedony. The term also covers translucent chalcedony varieties like moss agate, dendritic agate and phenomenal varieties like fire agate and iris agate. Agate has long been used to carve cameos, beads, cabochons, and decorative objects. Agate's name is derived from the site of its discovery, the river Achates (now Dirillo) in southwest Sicily.

General Information

  • Classification
  • Optical Properties
  • Characteristic Physical Properties
  • Chemistry & Crystallography
Common Name
Agate
Species
Quartz
Transparency
Translucent-Semitransparent
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
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
Chemical Name
silicon dioxide (aka silica)
Chemical Formula
SiO2
Crystal System
Trigonal
Chemistry Classification
Silicate

Agate Colors

  • Bi-color Agate
    Bi-color
  • Black Agate
    Black
  • Blue Agate
    Blue
  • Brown Agate
    Brown
  • Gray Agate
    Gray
  • Green Agate
    Green
  • Multi-color Agate
    Multi-color
  • Orange Agate
    Orange
  • Pink Agate
    Pink
  • Purple Agate
    Purple
  • Red Agate
    Red
  • White Agate
    White
  • Yellow Agate
    Yellow

Countries of Origin

Papua New Guinea; Angola; Kazakhstan; Paraguay; Portugal; Iceland; Armenia; Greece; Austria; Mongolia; Mozambique; Morocco; Unknown; Panama; Brazil; Algeria; Iraq; Chile; Lesotho; Argentina; Hungary; Isle of Man; Japan; Bolivia (Plurinational State of); India; New Zealand; Canada; Turkey; Belgium; Namibia; Faroe Islands; Finland; Italy; South Africa; Antarctica; Georgia; Jamaica; Peru; Turkmenistan; Ethiopia; Germany; Yemen; Afghanistan; Russian Federation; Viet Nam; Czechia; United States of America; Madagascar; Thailand; United Kingdom of Great Britain and Northern Ireland; Costa Rica; Sweden; Malawi; China; Poland; Slovakia; Bulgaria; France; Croatia; Romania; Sri Lanka; Uruguay; Timor-Leste; Kenya; Switzerland; Spain; Cuba; Norway; Botswana; Congo (the Democratic Republic of the); Mexico; Zimbabwe; Australia; Tajikistan

History

The first written account of agate was by Greek philosopher and naturalist Theophrastus (ca. 315 BCE) who mentioned in his book De Lapidibus (On Stones) that agate was named after the Achates River in Greece where it was found. The earliest known carved agates come from Mesopotamia. Carved animals that date back to between 2000 BCE to 1001 BCE have been found. The Mycenaean used agate for seals, cylinders, and jewelry. The Pylos Combat Agate was found in a Bronze Age grave that dates to 1450 BCE near the Palace of Nestor in Pylos, Greece. The Greeks and Romans used agate for signet rings and tableware. Agate was used frequently throughout the Middle Ages for decorative objects and the cutting industry in Idar and Oberstein, Germany was developed to take advantage of the quartz resources in the surrounding area. Agate continues to be popular today and is a favorite stone for modern day lapidaries.

Care

Normal care is recommended for agate except for dyed stones should not be exposed to ultrasonics, heat, or harsh cleaners.

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!

Species/Variety

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

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

Fortification or Banded Agate

Fortification or Banded Agates have nearly parallel alternating bands of color and is what most people think of as Agate. The most well-known varieties are Blue Lace Agate, Botswana Agate, and Laguna Agate.

Fortification or Banded Agate Agate
Fortification or Banded Agate Agate
  • Classification
Common Name
Fortification or Banded Agate

Plume Agate

Plume agates gets their name from its mineral inclusions that resemble feathers or billowy clouds of smoke. The best-known varieties of plume agate are Bloody Basin, Flame Plume, and Graveyard Point Plume agate.

Plume Agate Agate
Plume Agate Agate
  • Classification
Common Name
Plume Agate

Moss or Tube Agate

Moss and tube agates have inclusions that look like moss or enter connecting tubes. Some of the best-known varieties of moss and tube agates are Golden Moss, Indian Green Moss, Horse Canyon, and Rooster Tail agate.

Moss or Tube Agate Agate
Moss or Tube Agate Agate
  • Classification
Common Name
Moss or Tube Agate

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 Agate
  • Classification
  • Characteristic Physical properties
Common Name
Iris Agate
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.

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

Inclusions

Enhydro Agate

Enhydro agate is agate that has water in the central cavity.

Enhydro Agate Agate
Enhydro Agate Agate
  • Classification
  • Characteristic Physical properties
Common Name
Enhydro Agate
Toughness
Good

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

Sagenitic Agate

Sagenitic agate has networks of needle like minerals, embedded secondary crystals or crystal replacements. The term Sagenite comes from the Latin word sagena which translates to “large net”. Some of the best known sagenitic agates are Trent agate and Crazy Lace agate.

Sagenitic Agate Agate
Sagenitic Agate Agate
  • Classification
Common Name
Sagenitic Agate
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