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Agate is a cryptocrystalline variety of the mineral Quartz (SiO2).
Quartz is the most abundant single mineral on earth.
It makes up about 12% of the earth's crust, occurring in a wide variety
of igneous, metamorphic and sedimentary rocks.
Quartz varieties are commonly separated into two groups based on the
size of the individual grains or crystals;
macrocrystalline quartz in which individual crystals are distinguishable with the naked eye,
and cryptocrystalline quartz in which the individual crystals are too small to be easily distinguishable under the
Some of the macrocrystalline quartz varieties are:AmethystAmetrineCat's-eye QuartzCitrinePhantom Quartz CrystalRock CrystalRose QuartzRutilated QuartzSmoky Quartz
Blue Aventurine Quartz and the well-known lapidary material Green Aventurine Quartz
are both actually quartzites (a rock, not a mineral) composed essentially of interlocking
macrocrystalline quartz grains with disseminated grains of other color imparting minerals.
The cryptocrystalline varieties of quartz may be separated into two types;
fibrous and microgranular. Chalcedony is the general term
applied to the fibrous cryptocrystalline varieties.
Agate is an example of a fibrous cryptocystalline
banded chalcedony variety of quartz. Carnelian, Chrysoprase and bloodstone
are other chalcedony varieties.
Chert is the general term applied to the granular cryptocrystalline
varieties of quartz, of which flint and Jasper are examples.
Agate is a variety of chalcedony, which is the general term
applied to fibrous cryptocrystalline quartz varieties. It is a mineral generally
of secondary origin, forming in cavities and veins by deposition
from meteoric groundwater containing gelatinous silica from the weathering
of silicate minerals. It can also form by deposition from late
hydrothermal solutions at or near the
earth's surface under conditions of low temperature and low pressure.
Agate is commonly associated with siliceous volcanics, occurring as vein or
vesicle filling. It occurs as a petrifying agent in fossil wood and bone.
Agate is frequently found lining or filling rock cavities and fissures,
sometimes forming geodes.
Agate is characterized by its occurance, hardness, fracture, specific gravity,
refractive index and luster.
The name agate is from an old locality on the achate river in
Wearing agate jewelry has become very popular in recent times. Agate varieties have also been named for patterns or inclusions present in the agate such as lace agate jewelry, fire agate jewelry, banded agate jewelry, and moss agate jewelry.
Some agate varieties have been named for specific colors such as carnelian agate jewelry for orange-red agate jewelry items. There actually are dozens of named agate jewelry varieties!
Agate has been used as gemstones and other
ornamental objects for thousands of years.
In medieval times, the wearing of agate was said to bring
God's favor and make one agreeable and persuasive, giving victory and
strength to the wearer and protection from all dangers. Wearing agate was
also thought to give pleasant dreams and cure insomnia.
Early Greeks made amulets of agate for protection from the elements of the
Some of the earliest primitive
stone tools (axes) fashioned by man's ancestors 2.5 million years ago in the
Omo valley in Ethiopia, were made of quartz varieties such as agate. These
materials were used because
of their hardness and their isotropic brittleness which made it possible to
shape the tools with relative ease.
The astrological sign of agate is gemini.
Agate is a birthstone for the month of May.
Agate is the symbolic gemstone for the 12th
Agate is said to enhance
one's perceptiveness and to stimulate analytical capacity, and to provide
balance between one's physical, emotional, intelectual and spiritual states.
Agate is also said
to alleviate hostilities and promote goodwill.
Agate is said to help treat disorders of the pancreas
and to improve circulation.
For more in-depth metaphysical information, see our Metaphysical Books section.
Spectacular AgateDecorator Specimens