I have put myself into a problem. I have seen a rough stone sold by
several dealers as black nephrite jade from Austrailia. It has a
semi concoidal fracture. It is absolutely black, there is no green
on the edge of a wedge with no hint of transulency. It has no grain
as most nephrite does. I can break small chips off a corner with a
light tap with no hint of a fibrous structure. It is not nearly as
tough as any nephrite that I am familar with. It will take a
beautiful mirror polish.
The most distintive feacture is where a surface has weathered. It is
a solid red brick rust color.
My problem is that it is obviously not truly nephrite and I bought a
quantity of the material expecting that I could find a reference to
its true identity. So far, I have failed. Does anybody know what
this material is?
I know it isn’t nephrite, and I can’t sell it if I don’t know what
it is.
I’m in Australia and it sounds like a chert of some kind, but I
don’t/won’t guess at it. I’ll ask some of the local rock hounds for
you though.
You don’t happen to know where in Oz it might come from? Might help
to know as it will help to narrow things down some, remember
Australia is about the same size as the US (well lower 48
anyway)…
A couple of years ago at the Tucson Gem show I purchased some black
beads which I was assured by the seller were black jade,. In fact
that is what he wrote on my receipt. He said they were from China.
However, I was unable to Track down any on them. They
were pure black, and like yours had no grain. They did have a
beautiful finish. I asked an old rock hound about them,and he was
not sure what they were. Therefore, as I was uncertain about them,
and rather than mislead the customer, I sold them simply as Black
Stone Beads. As I used them instead of a chain, on which to suspend a
sterling pendant, I was able to charge enough to recoup my costs, as
they were quite expensive.
Another item which I purchased from the same gem show were several
strands of what were represented as natural aquamarine. They are a
pale green but with lots of black strands floating around in each
bead—sort of like dendrites… I have shown them to several people,
but no one seems to know what they are. They are nicely cut tube
shaped. As I rarely work with beads they have been waiting for me to
come up with some creative use for them, but will certainly not
represent them as aquamarine, unless I find out that they are indeed
as represented…
Hmmm. Good question. As for the rust red color, this is quite
possible with nephrite jade. I have seen a lot of California jade
with a rind that color. And black jade can be very dense. But the
cleavage sounds suspect. Hackley is the usual description.
Most likely, your black beads were schorl, the black variety of
tourmaline, which some times occurs in very large crystals, is easy
on the beading machines and takes a good polish.
The most distintive feacture is where a surface has weathered. It
is a solid red brick rust color.
Red streak is a diagnostic feature of hematite. Belong to trigonal
system, so your observation of brittleness fits. Should become
magnetic after heating density over 5, so specimens should have
noticeable heft
If you are getting a good polish you should be able to get an RI
reading. That will at least narrow it down. If you can’t do a SG test
maybe you can compare heft with known stones to put you in a
ballpark.
A couple of years ago I purchased some black cabs from a Russian
dealer who called them “black jade.” They actually turned out to be
jet. I found this out by doing the static test with wool, just like
what is done with amber. The cabs were op ague black, lightweight,
and when polished produced a brown/red debris. BTW, the cabs were not
popular as black jade. However, they had more value as jet since many
Native Americans use jet in their designs.
For stones/gems whose identities you are unsure of you might
consider taking them to a GG or FGA & asking for an ID… Many of them
can run a Refractive Index (RI), specific gravity test & other tests
that may positively ID the stone. If they cannot positively ID it,
they may be able to tell what it isn’t.
I am also the proud owner of a few hundred pounds of this material.
After polishing some test pieces, it does appear to be a jade.
A few years ago, I saw some photos of the original deposit in western
australia; it is an massive outcrop, and from the photos, yes, it
looked like what one might expect a jade deposit to look like.
red crust, brick red as you say, that formed in vertically oriented
joints in the deposit. stone rings like a bell, or resonates, when
struck. will hold a thin edge, fractures do not propagate, can
polish with alumina, diamond, chrome, although it can ‘apple peel’.
I would sure like to see an AA spectrometer reading to be sure.
I have also heard this material referred to as a massive tourmaline,
or a massive black schorl.
just have them tested by someone who has a gem testing machine
Ohh, ohh, I want one of them gem testing machines! (As far as I
know, the best “gem testing machine” is a gemologist or geologist
who works extensively with colored stones and minerals. Some of the
different tests a gemologist would do to eliminate what it isn’t,
and narrow the possibilities to what it might be, are refractive
index, birefringence, pleochroism, cleavage and fractures,
inclusions, absorption spectrum, fluorescence, specific gravity, and
streak. Some appraisers have the education and experience to do
this. If you are near one of GIA’s locations, you could take it
there and see if they can help you. If you are really interested,
take GIA’s colored stones Gem Identification course - fascinating!)
A few years ago I bought some large black cabs from a Russian dealer
who called them “black jade.” They were opaque, lightweight, and
produced a reddish brown debris when polished. I did the static test
on them and figured out they were probably jet.
There is a similar item being sold as Tibetan Black Jade. It is jet
black, high polish, and acts as you described. It is actually black
petrified wood…at least the samples I have seen. Not saying that
there isn’t any natural black jade from Tibet or Austrailia, but you
might give this some consideration. Good luck.
Thank you, everybody who has offered suggestions. I only have
comments on a couple of them to help narrow down the options. "Red
streak is a diagnostic feature of hematite. Belong to trigonal
system, so your observation of brittleness fits. Should become
magnetic after heating density over 5, so specimens should have
noticeable heft"I am certain that it is not hematite. The brick red
is the weathered surface, not a streak. The SG isn’t nearly as high
as hematite and the polished surface doesn’t have a metallic luster.
In fact, the polished surface is almost devoid of luster. It is
difficult to see the shape of the polished object except where there
are reflected highlights. "I’m in Australia and it sounds like a
chert of some kind, but I don’t/won’t guess at it. I’ll ask some of
the local rock hounds for you though."Thank you for your offer of
help. I think that my best chance is that someone who knows this
specific item will come forward. I am also certain that it isn’t
chert. It doesn’t have the glassy luster. If I had to hazard a guess,
it would have to be very fine grained basalt. Something like basinite
with lots of iron, if such a thing exists… I have never tried to
polish basinite and I got an excellent polish on this mystery
material. Still, I think that the most distinctive feature is the red
brick color where it weathers and that it is sold by several dealers
as black nephrite from Australia.
A few years ago I bought some large black cabs from a Russian
dealer who called them "black jade." They were opaque, lightweight,
and produced a reddish brown debris when polished. I did the static
test on them and figured out they were probably jet.
What you describe is probably Hematite and not Jet. I believe the
powdered and purified Hematite is the red polishing powder known as
rouge.
If I had to hazard a guess, it would have to be very fine grained
basalt. Something like basinite with lots of iron, if such a thing
exists.. I have never tried to polish basinite and I got an
excellent polish on this mystery material.
I’ve cut a lot of basinite as backing for opal doublets and
triplets. The truly fine-grained material takes a very good polish.
The weathered red “rind” doesn’t fit any basinite I’ve collected here
in the U.S. although it could be a secondary surface iron coating
deposited by water in cracks.
After writing the above I did a little searching on-line and found a
material being sold here in the U.S. that exactly matches your
description Email me and I’ll send you the URL to confirm it’s the
same. Maybe we can get some testing done.
Do not forget one of the best tests especially for opaque stones and
one of the most definitive tests is xray diffraction testsing which
tells one the chemcial breakdown of the stone for identification. You
may loose a very small piece of the black jade, a thumbnail, but it
will be a good identification.
These machines are very very expensive. Even state geology labs may
not have them or up to date ones. Several Univesrity labs may or may
nothave them. You can try John Attard of Attard Minerals In San
Diego California This testing is one of teh most definitive.
Also as the prinicpal of Heyden Gems, St Louis Mo, Dennis Heyden is
one of the formost peopel in jade. His Purple Jade Company is the
sole source for good pruple jade from Turkey. This jade has a
certian % jade in it which GIA then labeled Turkish Purple Jade.