Correct me if this summary of Nick’s posting is in error. Colour
variation in mineral-gems may be due to
(1) the geometry of crystallographic axes (perhaps C variations
would be an example); (2) chemical variations due to chemicals other
than those which define the mineral.
Under chemical variations there (a) elements and compounds (like Cr
in ruby or emerald) which impart colour and (b) ionic variations.
Variation in end-members IMO define a new mineral in a grouping as
in the feldspar grouping.
A standard field guide like the Audubon guide which I have here
glosses over the reasons for colour variations of most minerals
described but they are important as Nick illustrates in referring to
the cause of ruby and emerald colouration.
When the gem stone is a rock rather than mineral as is typical in
nephrite jade, Audubon gives a picture of nice, dark green jade rock
and then the associated text describes the mineral
actinolite-tremolite. But the colour variation may be even more
complex and varied because there could be scores of minerals in the
stone which give colour and pattern and Audubon is silent on this
What colour is pure actinolite-tremolite? Not rhetorical - does
anyone know? Has anyone seen pure or close to pure
actinolite-tremolite, eg in Smithsonian? I would guess at light green
or maybe even clear. But nephrite jade as a rock can be almost any
colour. In addition there are patterns as you can find in “marbled
jade” when included carbonates (of Ca and perhaps Mg) give a
As Elliot advised I had already sent samples to GIA and they are
good on identifying minerals but for more complex rocks like jade
rock, they advise petrographic analysis. I found the petrographic
analyses combined with assays of elements to be most helpful. Making
the calculations from Jade West nephrite assays of elements proved
that it was far less than 10% pure actinolite-tremolite.
What then determines the resulting colour of the final carved jade
other than the polish or light reflection in thin carved sections?
IMO it is the mixture of the many other minerals for the most part
and not the actinolite-tremolite. The actinolite-tremolite probably
imparts strength (toughness) to the rock as rebar imparts strength to
mortar or alpha pins to fire brick even though the rebar/pins are a
small part of the mass. You can see the fibrous minerals, sometimes
matted, in the petrographic photos.
Thus when it comes to the three gemological criteria of aesthetics,
rarity and durability the durability of nephrite jade may be
determined mainly by the “rebar effect” of actinolite-tremolite and
the colour may be determined mainly by scores of minerals other than
actinolite-tremolite. The value added to aesthetics by a world-class
carver may multiply the raw stone value by hundreds when an artistic
rarity is created. How much is a Bill Reid (Haida - Queen Carlotte
Islands First Nation) carving in humble argillaceous stone worth
after it becomes a totem figurine or a finely carved jewelry box lid?
The same could be done here in nephrite. A Sto:lo (Fraser Valley
First Nation) ethnogeologist believes the Sto:lo worked both nephrite
and argillaceous stone in centuries past. It became a lost craft in
Earlier an interest was expressed on Orchid re the Yang book with
its taxonomy of 44 jades. I located the book through a Chinese
translator and will post my findings when I get this file reader
working. Leaming seems to dismiss Yang since he says almost anything
can be called jade in a Chinese carving factory. But this may be a
Chinese-English translation problem. IOW Yang may be pointing to a
taxonomy of genuine actinolite-tremolite or jadeite jade or maybe
Leaming is correct and Yang may be saying any pretty and carvable
stone is jade.