I purchased a few pieces of “crab fire agate”. I’m beginning to
think this is not a stone at all. I got a message from a stonecutter
who had been cutting something similar, but he called it “spiderweb
carnelian”. Looking closely at the stones, I believe they are a
ceramic product with an unusual and clever glaze. When a hole has
been cut in a stone, for instance, the inside of the hole is a light
cream color, like a porcelain clay, and shows no color or
"snakeskin", “spiderweb” formation like the surface. Sometimes at the
very edges of a stone you see the same thing, as if a glaze had been
rubbed off at the edges or not applied there.
I think we have a complete fake on our hands here. Shades of
"rainbow calsilica".
Brian Corll
Brian Corll, Inc.
1002 East Simpson Street
Mechanicsburg, PA 17055
Hi Brian -
Upon reading your message I dug out some Chinese so-called
"fire-agate" beads that I’ve had laying around, dusted off my
microscope and refractometer…and the verdict is that this is most
likely chalcedony, not glass or ceramic.
Spot RI of 1.53
Layering and banding characteristic of chalcedony - very evenly
deposited linear bands or arcs with sharp, pointed intersections,
small pockets of druse in the centers of intersecting bands, just as
one would expect. Unlike banded glass, which has very swirled bands
and never a sharp intersection (at least that I’ve encountered). No
gas bubbles that I could find, and I spent an hour and a half
looking through the scope. Deep fractures that cut through the
banding, intersecting at 90 or 120 degree angles. No evidence of
filling or gunk inside that I could see, although there was often a
fine dusting of darker specks that appeared to be something that
might occur naturally in such cracks. There were some pieces with
small irregular black deposits, however - maybe a non-iron mineral
that doesn’t change with heat? Plus, some fascinating surface
fractures/crazing that resemble fractal patterns like crackle glazes
(I can see where you got the ceramic idea) or half-circle percussion
marks (fine, rust-red commas in the creamy layer). Indication of heat
treatment producing stress in the surface layer? Which surface layer
seems to be the creamy white stuff, as it tends to follow fractures
and overlay the carnelian below. I did get a good look down a bead
hole with the microscope’s fiberoptic light, and the inner layer was
definitely carnelian, not the creamy white material. An orange-peel
polish - OK, but not like the piece of Ocean Jasper I used as my
comparison piece when testing the refractometer.
That’s my story and I’m stickin’ with it…
Best regards,
Chris P.
Chris,
What bothered me was when I got the drilled piece and it showed a
creamy color inside the hole. Plus, the “crabbing” or "spiderwebbing"
looked very much as though it was just on the surface. I’m not at the
point yet where I can do sophisticated analysis (planning to do the
GIA GG course online) so I rely strictly on my eyes intuition, and
what knowledge I have gleaned so far in my new career. If it’s
chalcedony, that would jive with what I have heard from other people.
But I keep getting a different analysis from everyone person I ask.
I’m collecting opinions. I love a mystery, and in the gem world there
are plenty.
Brian Corll
Brian Corll, Inc.
1002 East Simpson Street
Mechanicsburg, PA 17055
Hi Brian -
We each may be looking at different materials, too - what you have
may not be what I have, even tho the names are similar. And that
crazed surface layer puzzles me - perhaps someone with more
familiarity with chalcedonies could weigh in on this? Any idea where
the rough comes from?
Staying tuned,
Chris P.
The secrecy of the origin bothers me, sort of like the “secret
source” for rainbow calsilica. Funny how this stuff is always
"discovered" in Mexico or South America.
Brian Corll
Brian Corll, Inc.
1002 East Simpson Street
Mechanicsburg, PA 17055
Funny how this stuff is always "discovered" in Mexico or South
America.......
I ran across a seller on ebay in the last day or so who referred to
this stuff as Brazilian, so there you go…
Carol
The secrecy of the origin bothers me, sort of like the "secret
source" for rainbow calsilica. Funny how this stuff is always
"discovered" in Mexico or South America.
Brian, that makes me suspicious, too. This material is very
fractured - brecciated - and, not being an expert in chalcedonies, I
keep wondering if it’s natural or the result of quench-crackling or
something. And that creamy surface layer is also bothersome because
of the way 1) it follows the fracture patterns; and 2) it’s crackled,
as if there were a coeffecient of expansion difference between it and
the carnelian below. Again, I don’t know if this phenomenon occurs
naturally.
However, the material is so inexpensive, I also have difficulty
believing that someone would go to the trouble to artificially crack
and fill it… But, like you, the Chinese lapidary industry has made
me far less trusting than I used to be.
Staying tuned,
Chris
the Chinese lapidary industry has made me far less trusting than I
used to be.
Your comment re the Chinese IMHO is completely unfounded. The Chines
have been extraordinary lapidarys for thousands of years.