CHALCEDONY – Microcrystalline variety of Quartz
in every imaginable color. The variety Agate is banded
in many different color combinations.
Chalcedony, being a microcrystalline
variety of Quartz,
does not occur in crystals. It occurs botryoidal,
as smooth rounded pebbles, as banded masses,
and in geodes.
waxy, or dull. Some yellow or brown varieties are resinous.
Many specimens fluoresce,
usually white or green
Chalcedonyx, Chalcedon, ChalcedoniteMicrocrystalline Quartz or Cryptocrystalline
Quartz (distinguishes Chalcedony fromcrystalline
are literally hundreds of variety names given to Quartz
and Chalcedony. Some are not scientifically recognized, but
are universally used. The important most important varieties
are listed below. All other variety names, including seldom-used
names, are listed in an individual page of Quartz and Chalcedony
varieties.These are the main varieties:Agate – Banded variety
– Reddish, transparent to translucent variety
– Banded variety
in which the banding
lines are straight and parallel, and consistent in band size.
– Opaque variety of Chalcedony that occurs in all colors.
Eye – Pseudomorph
of Quartz after fibrous
Chrysoprase – Apple-green variety
Bloodstone (or Heliotrope)
– Dark green to greenish blue variety dotted with small, red,
– Brownish to brownish-red, transparent to translucent variety
– Banded variety
with straight parallel bands of brownish to red alternating
with white or black bands.
uniformly colored variety that is somewhat impure.Scientifically, the term “Chalcedony” refers to any type of
Quartz. However, in the gem trade it describes a common white
or lightly colored nodular
of SiO2See also:
; Silica group
May also be classified as an oxide (Oxides ;
is not really known by its name. Scientist call it “Microcrystalline
Quartz”, and collectors and gem dealers call each variety by
its particular name. There are hundreds of different Chalcedony
varieties, and many have gem uses. In the gem trade, the name
Chalcedony describes white, lightly ,blue ,dep blue colored
The variety Agate
is most varied and popular of all Chalcedony. It is extremely
abundant and creates unusual and stunning examples. Most Agate
is ugly in a natural state. Specimens must be trimmed and polished
to bring out their full beauty. Most specimens sold to collectors
have already been treated, in the form of tumbled
stones or polished slabs.
Some Chalcedony is porous, and
it can be dyed different colors. Many Agate specimens from Brazil
are dyed, and are sold to the buyer without his knowledge of
this fact. With experience, one can usually tell by the color
of an Agate if it was dyed.
Chalcedony sometimes occurs in geodes,
lining the cavity with mammilary
blobs. Agate sometimes completely fills a geode cavity, forming
an Agate nodule
(sometimes improperly called an “Agate Geode”). Most Agate on
the market comes from these nodules.
information on geodes)Chalcedony frequently pseudomorphs
after organic materials. A well-known example is petrified
wood, wood that has been completely transformed into
Chalcedony (or one of several other minerals). In the Petrified
Forest National Monument in Arizona, an entire forest was transformed
into petrified wood. Remains of this ancient forest can be seen
in the huge silicafied
logs that are found in the area. Another well-known pseudomorph
is Chalcedony after coral. Underneath the Tampa Bay in Florida,
much coral has been replaced
by Chalcedony, and its original form is preserved.
Another Chalcedony pseudomorph is the famous “Tiger’s Eye“.
This almost legendary mineral has a most interesting and confusing
appearance. It is caused by a finely fibrous
structure of Crocidolite that was once present,
but has been transformed into Chalcedony through pseudomorphism.
are frequently present in Chalcedony. They may form a moss like
growth in the mineral, forming what is known as Moss Agate.
Another example is Dendritic Agate, a variety of Chalcedony
containing manganese oxide impurities that form fabrications
resembling trees. The “trees” may be strikingly realistic.
is an important ornamental stone. The varieties Agate, Chrysoprase,
Carnelian, Sard, Tiger’s Eye, Bloodstone, Jasper, and
Moss Agate are all carved into cabochons
and beads, making fine gems. The apple-green variety, Chrysoprase,
has a distinct color and commends a higher price than the other
varieties. Agate is carved into cameos and
ornamental objects, and is sometimes sold as polished slabs. Different
varieties of Chalcedony are tumbled
and sold to amateur collectors by the tons.
in hydrofluoric acid
hardness and crystal habits of Chalcedony distinguish it from
occurs in virtually all mineral environments,
and it may be associated with almost every mineral.
blue color Frequency: 606–668 THz
blue color Wavelength: 450–495 nm
|violet||668–789 THz||380–450 nm|
|blue||606–668 THz||450–495 nm|
|green||526–606 THz||495–570 nm|
|yellow||508–526 THz||570–590 nm|
|orange||484–508 THz||590–620 nm|
|red||400–484 THz||620–750 nm|