I remember being told, with regard to cryptocrystaline quartz stones, that if you can see through it, it's agate, and if you can't it's jasper
Thank you! I was beginning to feel completely nuts-- this is what I
was taught too. I hate giving misand I want to use the
correct terms for things, but it is starting to seem impossible.
Noel (in Chicago, where it has been snowing for about 16 hours now–
very unusual here, and no end in sight)
But to really be termed an agate it needs to have the banded structure of the fortification agates or brazilian agates.
If this were correct, then the term “banded agate” would be
redundant! There are plenty of things called agate that aren’t
banded… moss agate comes to mind. Sheesh, this sure turns into a
morass fast!
Noel
Since most dinosaur bone is opaque, shouldn't we refer to it as "jasperized"?
You could refer to it as ‘jasperized’ if you believe what you were
told is correct. Jasper is a subdivision of quartz. Does ‘jasperized’
explain anything?
For a fuller explanation see “Gem Cutting” by John Sinkankas.
KPK
But to really be termed an agate it needs to have the banded structure of the fortification agates or brazilian agates.
I would like to point out that while using cryptocrystalline quartz
is more accurate description of gem chrysocolla, it introduces more
limited understanding of the process than it has to be. Therefore, in
my opinion, using simply quartz is preferable for the reason that
native chrysocolla combines with many other minerals forming variety
of ornamental materials. Agatized chrysocolla is just one of the
many.
This is repetitious, but once again when we say that something was
agatized, it does not mean that it became an agate.
Leonid Surpin.
Helen.....ignore you? Sorry can't....you are an active participant and contributor to the overall worth of this great forum. In fact, thanks for being that.
Thank you very much Don. That’s very lovely of you. I enjoy reading
the daily digest and “chatting” with all the wonderful folk on the
forum and have learned so much as a result.
I do sometimes have bad days when nothing seems to go right and I
get frustrated, and such days are usually punctuated by many times of
having to assume the jewellers’ position to retrieve something
that’s jumped out of my butter fingers, whilst also being very
generous to my scrap pile! But I’ve learned that that is normal and
on such days, it’s better to stop fabricating and perhaps read some
of the vast material I have waiting to be digested instead. Then try
again tomorrow. I’ve never yet wanted to give up - it has to be the
most enjoyable of all the disciplines I’ve ever tried and this is one
I will NOT be giving up. In fact I’m rather excited this week because
although I’ve not yet tried to sell anything, I’ve had two people
wanting to commission me to make something for them (but nothing’s
written in stone yet) and today I’ve had my first definite order so
perhaps I’m doing something right.
Thanks for your kind words Don.
Helen
UK
It sounds a wonderful place John. I’ve owned and loved a lot of books
over the years, but my favourite by far was “Minerals, Rocks and
Fossils” which was given to me when I was about eight years old. I’ve
spent hundreds of hours pouring over that book so was fairly familiar
with Moh and his scale to a certain extent, but sadly I can’t find my
book anywhere and I’ve searched the house a few times! ;-( I wanted
to study geology at school but to do so you had to be one of the
chosen few who were good at geography and favourites of the geography
teachers. Sadly I didn’t fall into that category.
When I speak to Orchidians from the Rocky Mountains, I get ever so
slightly envious of the rich geological environment in which they
live. I’m currently looking into doing a little lapidary some time
soon so would love to live in such a place. I’ll have to settle for
buying rough on the internet I guess. My mum and dad live just down
the road from Lyme Regis though, which is famous for fossils and
they’ve sought out some ammonite fossils for me and would send me
more if asked I’m sure.
Helen
UK
but once again when we say that something was agatized, it does not mean that it became an agate.
That’s abuse of the english language. If you use ‘agatized’ that’s
exactly what that noun used as a verb ‘agatized’ means.
KPK
But to really be termed an agate it needs to have the banded structure of the fortification agates or brazilian agates.
The original post was correct, but simply vague.
Agates are classified into 2 large groups: Flat Parallel and Zonal
Concentric.
What commonly called banded agate belongs to Flat Parallel and
Brazilian agates are would be an example of Zonal Concentric.
About differences Agates and Jasper.
Agates form as a result of hydrothermal processes in igneous rocks,
and only found in the shapes called Amygdales ( geodes ). It is
interesting to note that in geology literature amethyst is called
amethyst agate.
Jaspers form as a result of regional metamorphism, contact
metamorphism, and hydro-thermal metasomatism. The later produces
material which can be confused with agate, but in generally lacks
agate structure.
So called moss agate is actually jasper with inclusions of chlorite.
The reasons why dino bones called agatized and not jasperized are
related to difference in formative processes of these 2 minerals.
Leonid Surpin
I remember being told, with regard to cryptocrystaline quartz stones, that if you can see through it, it's agate, and if you can't it's jasper
Regardless this is incorrect. People often pass along information
that is incorrect. Quartz is the gem material; agate is a subdivision
as is jasper.
Im beginning to feel completely nuts. I furnish accurate information
and it’s ignored.
Rather than word of mouth; did you ever play telephone as a kid; see
"Gem Cutting Jon Sinkankas if you are interested in accurate
KPK
While we’re agonizing over agate…moss agate certainly doesn’t
have bands; and what about crazy lace agate? (I suppose one could
rationalize it as being banded agate that got all shook up during
some early geologic cataclysm)
When I speak to Orchidians from the Rocky Mountains, I get ever so slightly envious of the rich geological environment in which they live.
Yep. I near one of the most interesting geologic formation. Of
course Garden of the Gods is the one most people think of with its
dramatic sandstone formations caused by sedimentary beds being raised
vertical by the up lift of the Pike Peak massif. But more interesting
to the geologists is the Pike Peak Batholith which is a triangular
area with Pike’s Peak being one point, the Cripple Creek area another
point, and the Crystal Peak/Lake George ares being the third. The
whole area was a mass of volcanic area which raised up the ground but
didn’t erupt, except for the Cripple Creek area that is a Precambrian
era volcano that gave deposited telluride’s gold and provided the
conditions to for turquoise. When the volcanic activity in the Pike’s
Peak Batholith receded it left all kinds of cavities or pockets in
the rock which allowed the Amazonite, Smokey quartz, Microcline, and
Topaz crystals to form.
In the same general vicinity there is the Florisant Fossil Beds
which boasts huge petrified tree trunks and a whole array of fossils
from a massive Cambrian era lake. It’s said the trees reached as tall
as today’s sequoias and redwoods. Most of them remain buried but
there are some that are unearthed. An interesting feature is the old
saw blades stuck in one petrified tree trunk when they tried to saw
it down to bring it to one of the early 1900’s Worlds Fairs.
All within 45 minute drive from my house. I’m treated with the view
of Pike’s Peak from my house in the winter when the neighborhood
leaves are off. But I only have to walk 1/2 block up or down my
street to see the whole view year round.
If I sound like I’m bragging I guess I am. I’m a proud Colorado
native. I was born here and intend to die here. Of course there are a
few things I would like to accomplish before the latter. Like figure
out Vista and Office 2007 for one…
Rick Copeland
Silversmith and Lapidary Artisan
Rocky Mountain Wonders
Colorado Springs, Colorado
rockymountainwonders.com
And I have often thought how wonderful it would be to live in a place
that had fossils. The only ones around here are some famous leaves
that still have their chlorophyl after many ages…besides um,
petrified wood, some of it opalized, but not precious opal. Opal has
some water losely attached to the silicon dioxide molecules, so the
surfaces are more vitreous than most wood replaced by the
cryptocrystalline quartz. Some of the replacements are really the
stuff to look at through microscopes for all the little individual
cells. But it also chips much more easily than the other stuff…a
litle iffy for intarsia.
Rose ALene
That's abuse of the english language. If you use 'agatized' that's exactly what that noun used as a verb 'agatized' means.
When process is described as agatized, but emphasis is made that the
final result is distinct from agate, the motivation is not to get
cute with English, but to say that formative processes were similar.
That requires an explanation.
Animal bone is composed of minerals and organics. Upon animal demise,
organics are destroyed very quickly by bacteria, leaving empty
spaces. These spaces, given the right conditions, are filled up with
minerals, which may or may not be quartz, but the process of filling
is similar to the process played out in agate formation.
These small spaces effectively become micro geodes, inside of which,
the crystallization of minerals take place layer by layer, in the
same manner like inside a regular geode.
Parallel to that, the mineral component of the bones is also
changing. In the presence of hydrothermal fluids, the metasomatic
processes insure that Calcium will be replaced with Silicon; so the
term silicification, which used sometime, is justified.
The resulting material is a conglomerate ( term loosely used ) of
nodules composed of different minerals, formed in agate like manner,
within a matrix of silicified bone.
So if someone asks how a dinosaur bone get look that way, I can give
long winded explanation as the one I used above, or I can simply say
that the bone was agatized.
Agatized is simply the most accurate description of the process
encoded in one word.
Leonid Surpin.
Cryptocrystalline quartz
Aventurine
Chalcedony
Agate (Any transparent or translucent chalcedony not called
Chalcedony)
Chalcedony (Any agate like material that is white, blue or gray).
Jasper (any opaque agate-like chalcedony).
Chalcedony nomenclature is colloquial and not scientific. I grew up
hunting for Ellensburg Blue Agate which is a Chalcedony and
Chalcedony proper but is called an agate. Carnelian is often a solid
color and is an Agate Chalcedony. Agate does not have to have bands
to be called agate (fortification agate if banded). I find a lot of
Jasp/Ag (jasper/agate mix) that is also a Chalcedony. The material
lining Amethyst Cathedrals from Brazil is Chalcedony, not agate
(solid blue-grey translucent).
Most Dinosaur Bone comes from the Moab, Utah area, to the best of my
knowledge. This material is most likely mostly calcite with trace
chalcedony and maybe some opal. I don’t know. I’m not a scientist,
just a cutter. I do suspect that fully fossilized bones have been
found in the world, as well as opalized remains. Just not from Moab.
Any organic matter that has been replaced my chalcedony is called
"fossilized". Any matter replaced my opal is “opalized”. We might
just say that dinosaur bone has been “preserved”. In my opinion I
would think “Dinosaur Bone” would be enough to call the material
because we all agree that’s what it is.
This material does not cut like any of the Chalcedonies. I suspect
it isn’t.
TL Goodwin
Agates form as a result of hydrothermal processes in igneous rocks, and only found in the shapes called Amygdales ( geodes ).
Not only amygdules; a few years ago I found an agate with concentric
carnelian banding that had formed within a cavity in a chunk of
milky white vein quartz. The agate is nothing much, but the unusual
occurrence is! I have not read of any other banded agate found here
in Virginia. I assume that hydrothermal processes transported the
silica and coloring minerals to the fracture zone while the vein was
still far underground. (Milky vein quartz is locally abundant locally
within the ancient phyllites that constitute the bedrock in my
neighborhood.)
Richard Davies
I already wrote today about some thoughts I have about this thread
(which is to say not many…) Check this out, though, from the
University of Nebraska:
http://snr.unl.edu/Data/agatepage.asp
USA had more than 250, Mexico and Canada each came up with more than
100 items - cool site and interesting, too. You may or may not note
what all is being called “agate”, too. In the rock world it’s much
like saying, “evergreen trees” in botany.
Chalcedony nomenclature is colloquial and not scientific.
Yeah, I had in mind to write something like what Todd wrote today.
It’s been interesting to see the contrast of those who learned
geology from books or from experience. The thing about rocks, as
opposed to minerals, is that nature wasn’t kind enough to supply us
with neatly categorized specimens. Translucent cryptocrystalline
quartz is agate if, when and because we (as a society) say it is,
otherwise it’s not. Kevin essentially said this long ago, and he was
correct. Quartz is quartz, yes. It can be truthfully said that
amethyst is not really quartz, because of the iron and aluminum that
colors it - that would be a chemist’s take, but geology isn’t that
anal about it - it is a variety of quartz. There are no lines, that
THIS is agate, and THIS is not (Of course, something that’s just not,
like chysocolla, for instance, just is not). I was out with a
geologist once and somebody picked up a rock and said, “So, what’s
this?” He said it was a rock. That the Earth gives us an endless
variety of them, and not everything is or can be categorized.
Sometimes a rock is just a rock, though it could be analyzed in a lab
to pin it down. Geology is science, to be sure, but it’s also an
inexact science due to the nature of the planet. I’ve been reading
this thread since it just kept bouncing back - all this
pseudo-science about what agate is. Agate is agate if, when and
because we (as a society) say it is. It’s not a scientific term, it’s
descriptive.
From the outset I will concede the point that for practical
applications, the distinction is without a difference, but since I am
a gemology geek, I would like to correct the following:
Chalcedony nomenclature is colloquial and not scientific.
There are 2 versions of origin of “Chalcedony”
First is ascribed to Georgius Agricola ( Georg Bauer ), who named it
after town of Calchedon near Istanbul. Second is that name was made
after Greek translation of Carthago (Carchedon), which was a seaport
used to transport it.
Jasper (any opaque agate-like chalcedony)
Jasper is metamorphic rock composed of Chalcedony, Opal, and
different admixtures.
Chalcedony (Any agate like material that is white, blue or gray).
Chalcedony is quartz which formed with cryptocrystalline structure.
There are several varieties of Chalcedony. Agate is one of them.
( Yes, I am aware that GIA nomenclature includes microcrystalline
quartz under Chalcedony. On that point I am in disagreement with my
alma mater. )
Agate (Any transparent or translucent chalcedony not called Chalcedony)
It may be O.K. to think that from a lapidary point view, or may be
not. As far as Gemology is concern, the definition is a bit loose and
backwards.
Leonid Surpin.
Not only amygdules; a few years ago I found an agate with concentric carnelian banding that had formed within a cavity in a chunk of milky white vein quartz.
You are absolutely correct !
I did what I am often accusing others of doing by using definition
which is to limited. Agate can form inside any cavity as long as
hydrothermal fluids are available.
Leonid Surpin.