Topaz or Quartz

[harry7777]

Hello all,

My Son and I recently found this piece at the Woolridge Fossicking area near Uralla, NSW. I think that it is Topaz or Quartz, it has two smooth sides which make it appear square from that perspective and a faint bluish colour.
Any help/opinions would be greatly appreciated. Thanks in advance.

 

[Pro-oz]

Two smooth sides, blueish tint, hold it up to your lip's topaz will be cold. I would say topaz.

 

[user 4386]

The best diagnostic method is to get a bit of quartz. Will it scratch the quartz?


Alternatively, topaz has a far higher specific gravity than quartz (3.55 rather than 2.65). It is easy enough to determine specific gravity if you have a suitable digital balance (but people seem to be scared off by the technique, ideal for a specimen like this). Search specific gravity under user 4386. It is a handy technique for many grains that people ask me about - zircon 4.65, sapphire and ruby 4.00 - all sufficiently different that most beginners will still be able to tell the difference. Diamond is 3.52 so similar to topaz, but FAR harder and commonly shows diagnostic crystal faces.

What is the source of the information that topaz will be cold if touched to the lips? I have only ever seen people say that on this website and have never heard it from a mineralogist or in any geology department at a university (and many worked with topaz). Perhaps only because it is so easy to tell the difference with hardness and often cleavage that they don't bother with it - I don't know. But I cannot think of any physical property of topaz that would make this occur. Can some gemmologists explain?

 

[Mackka]

Maybe it has something to do with the Larry and Curly Scale before it got to Moh?

 

[Pro-oz]

Haha, re topaz being cold, no scientific reason. Comes from and old tin miner friend out at O'Brians Mount Surprise.
Thought I may get shot down, but all good

 

[user 4386]

i.e. I would have thought Thermal Conductivity would be the main relevant variable, since its ability to draw heat from your lips would be what would give a sensation of coldness. However this is 3.5 W/m-K for zircon and 3.0 W/m-K for qartz, essentially no different.

I think the Specific Heat Capacity of zircon and quartz are similar (yet sapphire is twice as high but this property is never mentioned in identification).

Unfortunately I do not have any large enough lumps of zircon at present to do a meaningful comparison.

It is often mentioned on this site, not just by Peter, and I have always been dubious about it.

Might be comparable to the Blarney Stone story "The Blarney Stone (Irish: Cloch na Blarnan) is a block of Carboniferous limestone[1] built into the battlements of Blarney Castle, Blarney, about 8 kilometres (5 miles) from Cork, Ireland. According to legend, kissing the stone endows the kisser with the gift of the gab "