First, what is the material? Well, Peter Tovey of the Natural History Museum ten years ago did an analysis of powder from drilling a hole, and it consists of equal amounts of calcite and dolomite. So why the turquoise colour? I owe the answer to this question to my good friend Professor Alan Boyde. ‘Simple’, he said ‘it depends on Rayleigh diffraction’. If the particle size is around the wavelength of blue light, red is transmitted and blue diffracted.
The same phenomenon accounts for the turquoise colour of glazes on Tang Dynasty Changsha pottery. It depends on heating the glaze, and then cooling it slowly, so crystals of the right size form. A friend cut a wedge from a piece and embedded and polished it, and the crystals at the fringe of the wedge do transmit red light.
So an obvious question is, was this material originally white sedimentary rock that was then heated to over 400C, liquefied, and then cooled slowly so that crystals formed at the right rate? If so, was it also heated in the same impact event that produced the silica glass. Maybe the massive fires that followed the impact?
These coin-sized discs come in two diameters (from memory about 45 and 55 cm), and were turned, then cut manually and carved. The figures are rather crude, but some have Hongshan Icons on them. My guess is they were used as currency, being essentially useless, and hard to forge. The holes allow them to be carried round the waist with a threaded thong . Another interesting feature is that about half of them have characters carved on the obverse. Again, there is plenty of work here for an expert in ancient Chinese Scripts.
Finally, I have two discs in the same material that are around 20 cm across. Maybe the small ones were worth a pig, two for a cow, and the largest worth a wife or a house!
obverse of 18 with characters in relief
Large disc in same material
4 Characters on obverse
Another Large disc
Plaque in same material; note sample removed from one corner
Close-up of wedge embedded in plastic - note red fringe (left) where wedge is thinnest
Finally, three classic Hongshan Cloud pendante (one broken) in the same material
These three have a rather spidery C-dragon on them
This one a Hongshan Hawk
And this one a triangle of the same material in the central drill hole