Chalcedony or agate?

Jewelry Discussion
1

Hello

Long time lurker and lapidary here with a question for all you rock
minded folks out there.

I’ve heard it said that agate is banded chalcedony, i.e. all agate
is chalcedony but not all chalcedony is agate.

So if I cut a cabochon from a thick gemmy band within an agate so
that the finished gem has no bands, is it still agate or can it
properly now be called chalcedony?

I realize there may not be a correct answer but many opinions, I
await yours.

Thanks! Mark

2

I suppose, technically it would be called chalcedony. However, in
the trade there are other chalcedonies that are called agate.
Consider a moss agate, they very seldom have any banding with the
moss (it does happen in some thunder eggs) but they are always called
moss agate.

Rose Alene

3 
I realize there may not be a correct answer but many opinions, I
await yours.

John Sinkankas “Gem Cutting” It’s a matter of fact not opinion.

KPK

4

Variety. Therefore, all agate is Chalcedony, and when you cut an
agate to remove the banding, it is still Chalcedony.

Mariel

5

Hello Mark,

The name Chalcdone ist used -unfortunely- for the entire of fibrous
cryptocrystalline formed quarts group. Agate, chrysoprase,
heliotrope, jasper, carneolion, mosagate, petrified wood and many
others are a part of this group aswell as the real Chalcedone we know
as the white-bleu colored gemstone. The fiber-like form of chalcedone
(pointing to the real chalcedone) is most of the time the gemstone
we use to know behind this name.

The real chalcedone is formed by microscopic small fibers runing
parallel next to eatchother and is NOT banded. It is build-up by
stalactite kind of grapelike or kidney shaped forms. When it is
found in a banded appearance, it’s been called agate chalcedone. Real
agate however can be died in some kind of colors like Chalcedone. If
you look real close, you’ll see the differents due to the complete
dye of the agate which will absorb the blue color aswell.

My excuses for the improper way of writting this “explanation” but I
hope that it answers te question of what Chalcedone is ment to be.

Best regards
Pedro

6 
The name Chalcdone ist used -unfortunely- for the entire of
fibrous cryptocrystalline formed quarts group. Agate, chrysoprase,
heliotrope, jasper, carneolion, mosagate, petrified wood and many
others are a part of this group aswell as the real Chalcedone we
know as the white-bleu colored gemstone. The fiber-like form of
chalcedone (pointing to the real chalcedone) is most of the time
the gemstone we use to know behind this name.

The name Chalcedony comes to us from Agricola. One of the theories
is that material was named after city of Chalcedon where it was
mined.

Chalcedony is oxide of silica and water (SiO2 n*H2O, n varies ). The
material in “pure” form is translucent, slightly bluish-white. The
hint of blue is the result of Tyndall effect and not because of
presence of coloring agents.

If during formation other compounds are present, the result can be
Agate, Chrysoprase, and many other form of Chalcedony that are used
as So it can be said that Agate relates to Chalcedony in
the same way as Ruby relates to Corundum.

Leonid Surpin

7

Banding isn’t so much the issue anyway. Look at Carnelian, which
might be a solid color. If it’s banded it’s Sardonyx. Carnelian is
Agate. Agate is Chalcedony.

I think most consumers know “Agate”, and less know “Chalcedony”. At
least I find myself explaining it all the time. Traditionally it’s
chalcedony if it’s colorless or blue, but that is changing to
include lavender, purple, pink, green and even Orange. In that last
case it’s a case of renaming something that already has a name:
Carnelian! And Green Chalcedony is either Chrysoprase or Plasma. So,
It really does not matter if it’s Agate or Chalcedony anyway. No one
should be coming down on you for being wrong unless they really have
a sad home life.

Side note: Ellensburg Blue Agate is Chalcedony. Even though it is
blue, it’s still acceptable to call it “Agate”.

So, if it’s transparent or translucent and has no color, than it’s
chalcedony.

If it’s Orange, it’s either.

If it’s blue it might be either.

Anything else is agate, unless it if Opaque. Then it’s Jasper.
Unless it’'s opaque and translucent. Then it’s Jasper-Agate.

You could play it safe and just call it “cryptocrystalline quartz”.
No one can argue that point!

8 
The name Chalcdone ist used -unfortunely- for the entire of
fibrous cryptocrystalline formed quarts group. Agate, chrysoprase,
heliotrope, jasper, carneolion, mosagate, petrified wood and many
others are a part of this group aswell as the real Chalcedone we
know as the white-bleu colored gemstone. The fiber-like form of
chalcedone (pointing to the real chalcedone) is most of the time
the gemstone we use to know behind this name.

The name Chalcedony comes to us from Agricola. One of the theories
is that material was named after city of Chalcedon where it was
mined.

Chalcedony is oxide of silica and water (SiO2 n*H2O, n varies ). The
material in “pure” form is translucent, slightly bluish-white. The
hint of blue is the result of Tyndall effect and not because of
presence of coloring agents.

If during formation other compounds are present, the result can be
Agate, Chrysoprase, and many other form of Chalcedony that are used
as So it can be said that Agate relates to Chalcedony in
the same way as Ruby relates to Corundum.

Leonid Surpin

9

Thanks for your replies, personally I like the name chalcedony over
agate but use agate if it is commonly used like moss agate or
polka-dot agate (another un-banded “agate”) or proper like Brazilian,
Condor or Montana etc. The issue arose for me as I’ve recently cut
some blue chalcedony from Malawi that was seam agate but had thick
gemmy centers. Also from Mozambique I have some orange agate and rose
colored agate, all are banded often with white but have thick
translucent layers of color from which I cut cabs. Oh, and while on
the subject, someone recently asked about what caused the blue color
of blue chalcedony. It was stated to be the result of the Tyndall
effect. This may be the case for the Turkish Blue Mist chalcedony as
well as a typical Oregon thunder egg which can appear blue until you
cut off the outer rind, then the blue becomes slightly grayish. But
for the high grade Namibian material which is a rich almost purplish
blue, I cannot believe the color is the result of anything other than
some chemical makeup, perhaps iron. I’ve collected Holley Blue, pale
sky blue to beautiful deep purple, from basalt seams, surrounded by
iron rich orange clay.

Mark