Helios Red Helios Green Helios Blue Helios Purple

Lapidary / Gemstone Community Forum
March 28, 2017, 03:34:52 pm
Welcome, Guest. Please login or register.

Login with username, password and session length
News: This Forum has moved to a new host.  Please go to http://lapidaryforum.net/group/index.php and sign up so you can participate.  You will no longer be able to post here.  It is now a read-only archive.
 
  Home Help Search Classifieds Gallery Links Classified / Auctions Staff List Login Register  

Black Jade

Pages: 1 2 [3] 4  All   Go Down
  Print  
Author Topic: Black Jade  (Read 1646 times)
Amethyst Rose
Full Member
***
Offline Offline

Posts: 141


View Profile WWW
« Reply #30 on: December 18, 2015, 11:44:53 am »

One of the questions asked was that all nephrite is amphibole but not all amphiboles are nephrite.  This is correct as nephrite requires the amphibole crystals to be felted which is what give nephrite its strength.  If the crystals are elongated but not felted you will have an asbestiform variety of amphibole in the tremolite-actinolite solid solution series. 

So the answer is that nephrite is amphibole but not all amphiboles are nephrite.  It all depends on the formation.

Bob Johannes
The Amethyst Rose
BSc. Geological Engineering '85
Colorado School of Mines
Report Spam   Logged
vitzitziltecpatl
Hero Member
*****
Offline Offline

Posts: 696



View Profile WWW
« Reply #31 on: December 18, 2015, 04:15:41 pm »

Ah, so! Thank you. I wondered what made the difference - if it was a difference in the mineral makeup ("recipe"), or what. Your explanation helps crystalize (aaargh) this new knowledge within the rocky structures of my brain.

When you said "asbestiform" I looked up chrysotile, but see it's in the serpentine group. A completely different recipe. Thanks again.
Report Spam   Logged

Amethyst Rose
Full Member
***
Offline Offline

Posts: 141


View Profile WWW
« Reply #32 on: December 18, 2015, 04:47:14 pm »

The "asbestos" minerals are Chrysotile which is a serpentine and the amphiboles; Tremolite, Actinolite, Crocidolite, Anthophyllite, and "Amosite" which is actually the solid solution series cummingtonite-grunerite.  There was a battle a few years ago during the clean-up of Libby Montana as to whether or not the Libby amphibole could be called asbestos as it was not tremolite or actinolite but one of the defined minerals in the solid solution series.  EPA won that one so any amphibole with releasable fiber greater than 5 microns long and a 3 to 1 aspect ratio is asbestos per the EPA's regulations.  I know all this as I have been a state asbestos regulator for the last 24 years.

Some of the material I have seen sold as ghost jade would probably be classified as asbestos under the regulations.  Most "nephrite" has too tight a felted structure to release fibers so cannot be classified as asbestos.

Bob Johannes
The Amethyst Rose
Report Spam   Logged
Talusman
Sr. Member
****
Offline Offline

Gender: Male
Posts: 418


View Profile
« Reply #33 on: December 18, 2015, 05:22:50 pm »

How does this Australian material factor into this discussion? For sale on thegemshop's site - says it's comparable to Edward's Black and is "Nephritic".

-Jeremy

http://thegemshop.com/collections/rough-rock-1/products/black-jade

Report Spam   Logged
Michael S Hoover - Redrummd
Hero Member
*****
Offline Offline

Gender: Male
Posts: 1647


Art In Stone


View Profile WWW
« Reply #34 on: December 18, 2015, 05:43:07 pm »

The fracture line and grain does not look like any I have seen on Nephrite.  It is very difficult to be definitive from a photo.
Report Spam   Logged

finegemdesigns
Sr. Member
****
Offline Offline

Gender: Male
Posts: 445



View Profile WWW
« Reply #35 on: December 18, 2015, 06:37:52 pm »

"The definition of nephrite is even more controversial. Mineralogy texts have traditionally listed nephrite as a variety of actinolite, a monoclinic member of the amphibole group. As in the case of jadeite, however, actinolite is very closely related chemically and structurally to other members of its group. Actinolite [Ca(Mg,Fe),(SiO,),] is so closely related to tremolite [CaMg, (SiO,),] that their optical and physical properties may be indistinguishable. The magnesium in tremolite is commonly replaced by iron, and the two minerals do, in fact, grade into one another. The color of the material. however. indicates the amount of iron present: the iron in actinolite imparts a green to grayish-green color, whereas the iron-poor tremolite is normally white to gray. The fact that nephrite is, in reality, a variety of two mineral species recently led the International Mineralogical Association (I.M.A.) to discredit nephrite as a valid mineralogical variety."

Source: THE JADE ENIGMA By: Jill M. Hobbs

"Although nephrite has been "discredited" so far as referring to any known mineral species by the CNMMN [Commission on New Minerals and Mineral Names] of the IMA [International Mineralogical Association], it seems likely that it will persist in the world of gemology."

Source: http://www.dolphingems.com/Completeview.aspx?code=Nephrite_Jade&cat=Gemstones&subcat=Stones

And here is the International Mineralogical Association website with complete list of minerals:

http://nrmima.nrm.se/

So this supports my earlier contention about "nephrite" in agreement with Glen Laidlaw:

 "It is a GENERAL descriptive term"

Glenn Laidlaw (wrminerals) Wind River Minerals
Glenn Laidlaw (quoted above) has 35 years of experience with Wyoming minerals and had some Edwards Black Jade analyzed on two separate occasions.
Report Spam   Logged



vitzitziltecpatl
Hero Member
*****
Offline Offline

Posts: 696



View Profile WWW
« Reply #36 on: December 18, 2015, 07:08:30 pm »

So - in general terms - anything that fits into the parameters of the GIA fact sheet info is in fact "nephrite" jade?
Report Spam   Logged

55fossil
Sr. Member
****
Offline Offline

Posts: 272


View Profile
« Reply #37 on: December 19, 2015, 07:01:21 am »

Bob;    Could you explain your statement " If the crystals are elongated but not felted you will have an asbestiform variety of amphibole in the tremolite-actinolite solid solution series. As you can see in the pictures I attached I had jade that crumbled in the saw. When I turned it to cut with the grain it was excellent and made great cabochons. Mike H. explained to me this is not all that uncommon in lower grade jades. I am just concerned this could contain asbestos and be dangerous.


* IMG_7664.JPG (3159.96 KB, 3456x2304 - viewed 9 times.)

* IMG_7666.JPG (2734 KB, 3456x2304 - viewed 5 times.)
Report Spam   Logged

Amethyst Rose
Full Member
***
Offline Offline

Posts: 141


View Profile WWW
« Reply #38 on: December 20, 2015, 07:55:36 am »

55fossil,

I would describe the block in question as having layers of felting with weak layers in between.  This causes it to break up when cut across the layers but hold together when cut with the layers. 

I would not consider this to be dangerous as ling as it is worked wet as any amphibole should be or with the use of appropriate breathing protection; a well fit respirator with p100 filters.  The P100 are specifically designed to filter out asbestos fibers and are effective to 99.97% of all particles 0.3 microns or greater.  They will also filter out viruses.

Glad you were able to get some good stone out of the block, it have lovely color.

Bob Johannes
The Amethyst Rose
Report Spam   Logged
southerly
Hero Member
*****
Offline Offline

Posts: 1090



View Profile
« Reply #39 on: January 06, 2016, 04:13:48 am »

Nephrite is problematic in definition (jadeite is not immune either). Most gemstones are minerals and as such are defined by their chemical composition, eg rubies being corundum with chromium as the colouring agent. Minerals have a specific chemical composition (with some variabilily where one element substitutes for anther in a series) that can be determined the XRD and other methods. Rocks are distinguished from minerals in that they are made up of a combination of minerals, this can be obvious in the case of granite where each mineral is present as discrete crystals, or as a mixture of minerals as is typical with serpentinite.

The problem with nephrite is that it is defined by the physical characteristics of the rock, specifically toughness due to felting of the crystals in the rock. Usually nephrite is defined as a combination of actinolite and tremolite where the crystals ave felted together. If not fully felted the rock will fall apart when cut. Actinolite and tremolite can exist together and not be nephrite if the felting is not present. Whether pure actinolite or tremolite can be nephrite has long been debated. This is further complicated by the fact that a rock can grade in and out of nephrite in a single piece.

If I understand Finegems argument correctly, he is stating that since nephrite does not have a specific chemical composition (is not a mineral) it does not exist, and points to the GIA's reluctance to identify nephrite as proof. That the mineral naming organisations do not recognise nephrite is not surprising as it is a not a mineral it is a rock.

The term jade was in common usage several thousand years before XRD was invented. It's generally accepted use is good enough for me, though I expect the arguments will rage forever.

Jadeite is sometimes referred to as the only 'true' jade (often by jadeite sellers) as it is an identified mineral with a specific chemical composition. However it is also problematic for two reasons, firstly the GIA in testing discovered that some gem quality jadeite was actually the related mineral omphacite, hence their inclusion of omphacite under the heading of "jade" (if they did not do this many of the certificates they previously issued would be invalid, plus gem quality jadeite and omphacite at least once cut can only be differentiated via XRD. Secondly, jadeite itself rarely occurs in pure form, jadeite rocks are commonly a mixture of jadeite, omphacite, other pyroxenes and other minerals such as feldspar and quartz. So a problem for jadeite is what percentage of jadeite is required to call a rock "jade", Google the technical papers on Turkish purple jadeite for examples, Guatemalan jadeite is also commonly a mix.

So for me, jade is by definition a historic term that refers to rocks that have a toughness that exceeds all other rocks (btw nephrite is tougher than jadeite due to the felting of the crystals, in jadeite the crystals are interlocking but not felted) therefore I am happy referring to nephrite and jadeite as jade.

David
Report Spam   Logged
finegemdesigns
Sr. Member
****
Offline Offline

Gender: Male
Posts: 445



View Profile WWW
« Reply #40 on: January 06, 2016, 02:07:57 pm »

Thanks for posting southerly. This is probably the best explanation. The key is the felting which gives the rocks their toughness and ability to be carved into thin pieces and sculptures.

Of course this felting can't be quantified/qualified 100% and used to define which amphibole is "nephrite jade" and which is not "nephrite jade."

There is no scientific dividing line which defines jade by it's percent of felting.

At least not to my knowledge at this time.

BTW I still have your awesome quote on my website.

http://www.finegemdesigns.com/blackjadesprojectpage3.htm

:o)
Report Spam   Logged



Michael S Hoover - Redrummd
Hero Member
*****
Offline Offline

Gender: Male
Posts: 1647


Art In Stone


View Profile WWW
« Reply #41 on: January 06, 2016, 10:53:20 pm »

Edwards Black on a Case peanut finished yesterday - sold today.....



* Redrummd 2387PCS B.JPG (460.41 KB, 1785x1230 - viewed 8 times.)

* Redrummd 2387PCS G.JPG (388.84 KB, 1966x896 - viewed 8 times.)

* Redrummd 2387PCS L.JPG (319.27 KB, 1718x829 - viewed 4 times.)

* Redrummd 2387PCS I.JPG (417.11 KB, 2038x1084 - viewed 4 times.)
Report Spam   Logged

finegemdesigns
Sr. Member
****
Offline Offline

Gender: Male
Posts: 445



View Profile WWW
« Reply #42 on: January 06, 2016, 11:31:14 pm »

Well done.

 dancer7
Report Spam   Logged



southerly
Hero Member
*****
Offline Offline

Posts: 1090



View Profile
« Reply #43 on: January 07, 2016, 12:10:10 am »

Great looking knife Michael.
Report Spam   Logged
southerly
Hero Member
*****
Offline Offline

Posts: 1090



View Profile
« Reply #44 on: January 07, 2016, 12:17:18 am »

BTW.. lapis lazuli is also a rock not a mineral, with variable composition, made up of lazurite, sodalite, calcite and pyrite, in varying concentrations which create the different grades of lapis and also suffers from the problem of when does the lazurite percentage become too low to call it lapis lazuli?
Report Spam   Logged


Pages: 1 2 [3] 4  All   Go Up
  Print  
 
Jump to:  

Powered by EzPortal
Bookmark this site! | Upgrade This Forum
SMF For Free - Create your own Forum | Buy traffic for your forum/website

Powered by SMF | SMF © 2016, Simple Machines