JJHerb@aol.com on sat 28 dec 96
"Incidentally, Aluminum Oxide crystals with small levels of impurity are
found occurring naturally as ruby, emerald, topaz, sapphire and amethyst in
addition to the corundum mentioned earlier."
In the interest of mineralogical accuracy: Amethyst is a variety of quartz,
SiO2, as is flint, also called jasper, chalcedony, and agate, depending on
color. Topaz is an alumino-fluro-hydro silicate - (AlF)2 SiO4 or
[Al(F2+OH)}2 SiO4. Emerald is a chrome bearing variety of the mineral Beryl,
Be3Al2 (SiO3)6. Beryl crystals are six sided, reflecting the ring-shape of
the beryl "molecule".
Corundum, the general mineral name for naturally occurring aluminum oxide, is
called by the gem names sapphire when blue and ruby when red. Dana s
Textbook of Mineralogy also lists the names "Oriental Emerald, Oriental
Topaz, and Oriental Amethyst" for corundum that is green, yellow, or purple.
When black it is called emery. The mineral Spinel FeO Cr2O3 occurs in a red
variety that has been called ruby in the past.
The gem names, which have never been very rigorously applied, are corrupted
by the practice of "creating" gem stones which are then named. This started,
on a large scale, with the Linde star sapphires (corundum) and has expanded
to include "Lab" emeralds, etc. An advantage of the green corundum over the
green beryl is its hardness - 9 as compared to 7.5-8. The same thing applies
to the yellow corundum over the yellow topaz - 9 as compared to 8, and to
purple corundum over purple quartz, 9 to 7. Real topaz and beryl do seem to
occur in larger crystals than does corundum. The Smithsonian has a 22,000
carat topaz - about the size of an American football (Go Browns). Beryl
crystals six feet in diameter and many feet long have been discovered. These
were not of gem quality but interesting anyway.
Joseph Herbert
JJHerb@aol.com
kevin_hulmes@uk.ibm.com on mon 30 dec 96
Ref Joseph Herbert's post of Sat 28 Dec.....
Joseph, thanks for your detailed clarification on the above. My source
for listing the Aluminium Oxide gems was a well respected Chemistry text,
and although I was surprised (especially with Amethyst), I didn't
bother to check its validity. I guess it wasn't quite incorrect, but I
prefer your analysis, which reflects the more widely understood position.
PS: You sure know how to make a fella feel old! .......
<"In olden times, a manometer might contain mercury">
.... Kevin
*--------------------------------------------------
* INTERNET: kevin_hulmes@uk.ibm.com
* Phone/Fax/Msgs (0)1926 887003 (UK)
*__________________________________________________
| |
|
