[Rockhounds] Chinese Crystals on E-Bay

[jbacko]

Lawrence Rush wrote:
> If the crystal looks absolutely clear, with no imperfections, and is 
> perfectly terminated, it may be one of the "manufactured" ones. Some 
> are colored red, and are very even in color appearance. Some are 
> perfectly doubly terminated. I have heard that they are made by 
> melting and casting silica, but I have no first-hand experience. 
> Unfortunately, these days, much from China must be viewed with 
> skepticism.
>
A large un-twinned NATURAL  quartz crystal that is also very clear must 
always be suspect without provenance, because they are very uncommon. 
Manufacturing ("growing") large quartz is common, and is the source for 
almost all of  the quartz used in electronics, etc. It is manufactured 
because twinned quartz crystals cannot be used in electronics. Which is 
one of the reasons that the Arkansas quartz is still so abundant and 
mostly not tied up in commercial, industrial mining. Also, the crystal 
would have to show a fracture on the bottom where it was broken form the 
matrix, or a second termination point. A natural doubly-terminated 
crystal would almost certainly show a flaw somewhere along the c-axis as 
it was attached to the matrix there. Even Herkimer quartz shows a lot of 
these flaws.  The crystal does not grow in a vacuum; it has to be 
attached somewhere.

A cheaper quartz "crystalline material" could be made from fusing 
silica, but it would almost certainly be a type of glass. It too is 
quite common because it is used in the manufacture of optics and lenses. 
However, in this case, the crystal would have to be manufactured as well.

Refractive Index is the surest way to tell the difference. That and 
specific gravity. As a quick comparison perhaps, take a small but 
perfect real quartz crystal and the big one and cast a spectrum through 
them from sunlight. If they are the same material, the two spectra 
should be pretty close to identical.

> Also, watch out for "Zircon" from China in large, well formed 
> transparent crystals. These are also reputed to be manufactured. Rock 
> Currier may have more first-hand experience than do I (?).
>
> Larry Rush
>



john