Agates
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Museum Specimens
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Most agates occur as nodules in volcanic rocks or lava flows. Agates are formed in cavities produced by gas
bubbles in the molten magma. These cavities are filled by siliceous materials that are deposited in regular
layers upon the walls. Agate can also be found as a veins or layers that formed in voids or cracks in volcanic or  
rock fractured by intrusive masses. When agates are cut you can find a succession of very thin parallel lines
giving a banded appearance to the agate. Such stones are known as banded agate, riband agate and striped
agate.

During the formation of the agate waters containing silica percolated through the rock and deposited a
siliceous coating on the interior of the cavities. Changes in the mineral solution, or in the conditions which they
are deposited, can cause a mineral variation in the layers. Bands of chalcedony often alternate with layers of
crystalline quartz. Several gas bubbles may join and form large cavities in the magma and lava. This is how
large amethyst geodes are formed.

Agates may be found in various kinds of rock, they are normally associated with volcanic rocks but can be
common in certain metamorphic rocks.  They form in concentric layers and fill cavities in a host rock. The
results are round nodules bands similar to tree trunks and may appear as eyes, scallops, or as landscapes
with dendrites that look like trees. This last type is called Tree Agate or Moss Agate. Many fossils are actually
agatized material that replaced an organic substance such as wood. Many varieties of petrified wood are
examples where the original structure has been replaced with agate.

The word Agate comes from the Greek name for a stone originally found in the Achates River in Sicily (currently
known as the Dirillo River). Agate has been found with the remains of Stone Age man in France from as early
as 20,000-16,000 BC and the Egyptians used agates prior to 3000 BC for talismans, amulets, seals, rings and
vessels. Early civilizations used eye beads to protect them from evil and bring good luck. They created eye
beads by carving a hole through an agate disc.

Although agate is found all over the world, the most exceptional specimens come from Southern Brazil and
Northern Uruguay. However, the moss agates of Colorado and Montana are equal in beauty and some
beautiful specimens have been found in Mexico and California. A geode type of agate, called
"Thunder Egg"
by Native American Indians, is found in Oregon. Fire agates come from Mexico and Arizona. Deposits exist in
China, Mexico, India, Madagascar, and the USA along the shores of Lake Superior.  Agates are found all over
the world wherever highly pressurized hot water rich in silica filled crevices and vugs. Often tiny quartz crystals
form within the stone and add to the beauty and uniqueness of individual stones. These crystals are called
drusy (sometimes misspelled as druzy).

The outer surface of an agate is rough, pitted and ugly. It hides the beauty of the crystal inside. However, the
crust is weak and somewhat fragile and over centuries it is washed away allowing the gemstone to be
discovered along rivers and streams.
Agate occurs in most colors including black, gray, brown, reddish, green, pink, blue, and yellow from
transparent to opaque. Today, many of these stones are artificially dyed to enhance the depth of color and to
produce more vivid tones than those found in nature. If you think the specimen you are looking at is dyed rather
than natural don’t be afraid to ask. Reputable sellers always list whether an agate is dyed or natural. There are
thousands of localities worldwide where agate specimens have been found, many of these are named for the
locality. Some areas with exceptionally beautiful specimens have been depleted by over mining, but because
agate is so common there are usually several new discoveries each year.

The following is only a partial listing of the most commonly known varieties:
Banded Agate, Blue Agate, Blue Lace Agate, Botswana Agate, Brecciated Agate, Carnelian Agate, Cloud
Agate, Crazy Lace Agate, Dendritic Agate, Fire Agate, Green Agate, Indian Agate, Laguna Agate, Mexican
Lace Agate, Montana Agate, Moss Agate, Nipomo Agate, Oregon Snake skin Agate, Picture Agate, Plume
Agate, Pom Pom Agate, Rainbow Agate, Russian Agate, Sagenite Agate, Sweetwater Agate, Sonoran
Agate, Tree Agate, Wood Agate, Tube Agate, and Turretella Agate.

The hobby of collecting bowls made of agate was popular during the renaissance and this activity was
responsible for the growth of the lapidary industry near Idar-Oberstein in Germany. Although agate beds were
originally found in that area, most of the local deposits were depleted in the nineteenth century. Today the
majority of the agate sold in Idar-Oberstein is actually imported from Brazil. (Native
Idar-Oberstein agates are
highly sought after and are becoming very valuable)

Many Gem and Mineral shows sponsor old time rock hounds that bring hundreds of geodes to break open with
a specially made tool that splits the geode open leaving the internal material undamaged. Crowds that gather
at his booth pay their money, in hopes of owning a beautiful specimen full of amethyst or citrine crystals. Agate
geodes can be very small or very large. The largest geode ever mined was found in Brazil and weighed almost
two tons.
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Rare Scottish Pink Banded Agate
This natural pink banded agate with a quartz crystalline center was acquired in 2009 from a
mineral dealer at the Quartzite, Arizona Gem and Mineral Show. This beautiful agate specimen
nodule half is polished and is from the Ardownie Quarry  located in Dundee, Scotland.

measures 2 x 1.3 x 0.7 inches (52 x 35 x 17 mm) and weighs 36.5g
Item # SCAG11156341
Rare Scottish Pink
Banded Agate

$29.00