MAJOR WORLD OCCURANCES OF SAPPHIRES
Kashmir
Color : Cornflowerblue
with sleepy or hazy appearance due to clouds and milky bands. Mostly
natural color considered to be the finest.
Identifying characteristics :
Velvety texture, sharp blue whitish zoning, dust-like inclusions
of rut called " snowflakes" corroded zircon crystals with
accompanying black uranite, black uranite crystals, tourmaline and
pargasite crystals.
Heat treatment : Attempts to improve transparency
and appearance have not been very successful. Some milky/silky gray
material could turn to beautiful blue color (25-30%)
Miscellaneous : Mining at 4500 meters stopped
because of the war, so stone are rare
Burma
Rich, dark, intense color described as “Royal blue” due to scattering
of light from fine “silk”. Mostly naturally color when is top quality,
slightly lower than Kashmir.
Color :
Heat treatment : Calcite
inclusions are a problem for obtaining good color. About 60-70%
fine to very fine material in market is heated.
Miscellaneous : Ruby
is 80% of the total output from Burma.
Sri Lanka
Color : Lighter
in color called "Ceylon" in the trade. Other colors than
blue are possible including care orange-pink known in the trade
as "Padparasha "
Identifying characteristics
: Dense clouds of long rutile needles fine "fingerprints"
(heated fractures), zircon and negative crystals, characteristic
strong zoning. Often with chromium spectrum and reddish fluorescence
due to chromium impurity.
Heat treatment :
typically 40% of the recovered corundum is heat - treatable grade
sapphire. Results are good so about 80% of fine quality material
is heat treated.
Miscellaneous : Major source of fine blue
sapphire due to successful heat treatment.
Mardagascar
Color : Similar
to Sri Lanka stones only darker. All colors of the rainbow are possible.
Identifying characteristics
: Strong zoning numerous small crystals. Magnetite
octahedral crystals.
Heat treatment : Colorless
pieces with blue core suitable for heat treatment (80-90% on the
market)
Miscellaneous :
Important source since 1994.
Thailand/Cambodia
Color : Deep
blue, somewhat inky in Kanchanaburi, but rich and lighter in Palin
(Cambodia)
Heat treatment : almost all commercial quality
stones are heated to lighten the color.
Identifying characteristics
: Long boehmite white needles, minute rutile silk,
hematite silk, plagioclase feldspar, red crystals of uranium pyroclore
(Pialin), anagular color zoning strong ion spectra. (450 mm)
Heat treatment : 90-100%
of top commercial quality material is heat treated and may be diffusion
treated.
Miscellaneous : Chanthaburi
area produces predominately rubies, yellow sapphire and black star
sapphire.
Australia
Color : Dark
blue, inky called "midnight blue" even after heat treatment.
Identifying characeristics:
"fingerprints" (secondary heated
fractures), ilmenite and hematite needles and plates, strong zoning
strong green dichroic color, strong iron spectra.
Heat treatment : Almost
all commercial quality stones are heated to lighten the color.
Miscellaneous :
Sapphire was first discovered in the later 1800's in both northern
NSW and central Queensland. Early mining mainly took place in Queensland
where by 1930 two ton of sapphire had been produced, mainly sold
to German buyers.
After World War I production was very small until 1960's when mining
at both fields really expanded dramatically due mainly to demand
from visiting Thai buyers. The Thais have been and still responsible
for marketing of almost all cut the Australian sapphire produced.
Note : Other
sources of sapphires are Brazil, Colombia, India, Nigeria, Montana,
Tanzania, and Vietnam etc.
Most
of the sapphires from South East Asia, Africa and Australia are
heat treated in Bangkok and Chantaburi. Thai heat-treaters use a
conventional diesel-fueled furnace that can reach temperatures of
around 1,700 degrees Celsius in a reducing environment. Specific
details of the process are still guarded secrets in Thailand, and
while the outcome is not totally predictable the resulting colors
are usually an improvement. In Sri Lanka, gas furnaces are widely
used to heat corundum in a primarily oxidizing environment and the
results are met with varying degrees of success. From experience,
heat-treaters know at what temperatures geuda material converts
to blue sapphires, however, the trade generally does not understand
the science involved in the color changes.
Summary of the heat treatment process
using the Thai "Condor" furnace:
1) Diesel, Milky, Silky Dun and Ottu geuda requires reducing conditions
to develop blue. The blue color is due to Fe Ti change transfer
with the absorption of energy at 450 mm. to develop (Fe2+)
+ (Ti4+) = (Fe3+) + (Ti3+)
Intensity of the blue color has a direct correlation to the Ti
content (1% total) present in rutile needles.
Summary of the heat treatment process
using the Sri Lanka "Lakmini" gas furnace.
1) Bluish red pink and yellow geuda need oxidizing conditions
to eliminate blue color and intensify red and
yellow color.
(Fe3+) --> (Fe2+)
Blue sapphire is the most popular gemstone in the United State
of America. Thailand is the biggest exporter to the USA. The major
sapphires suppliers to USA are as follows.
U.S.
GENERAL IMPORTS OF MERCHANDIES
Commodity by Country, Commodity Code w/Description
710390020 SAQPPHIRES CUT BUT NOT FOR JEWELRY
Time Period 2000 Annual (Value = $) |
Country
|
Quantity
(CAR) |
Value |
| CANNADA |
699 |
602,506 |
| BRITISH VIRGIN |
416 |
173,250 |
| COLOMBIA |
43,096 |
103,031 |
| BRAZIL |
6,587 |
158,052 |
| UNITED KINGDOM |
13,792 |
2,809,392 |
| BELGIUM |
2,995 |
498,526 |
| FRANCE |
1,741 |
863,758 |
| GERMANY |
53,715 |
1,396,877 |
| AUSTRIA |
5,881 |
658,877 |
| SWITZERLAND |
50,388 |
16,786,881 |
| ITALY |
10,077 |
587,803 |
| ISRAEL |
63,055 |
5,096,232 |
| ARAB EMIRATES |
3,719 |
548,375 |
| INDIA |
1,158,812 |
3,562,216 |
| SRI LANKA |
491,956 |
25,068,430 |
| BURMA |
8,719 |
2,165,566 |
| THAILAND |
6,003,123 |
81,083,660 |
| SINGAPORE |
147 |
129,000 |
| CHINA |
29,964 |
71,227 |
| HONG KONG |
326,303 |
10,778,307 |
| TAIWAN |
1,603 |
421,880 |
| JAPAN |
104,778 |
826,977 |
| AUSTRALIA |
7,321 |
752,476 |
|
| References: |
| 1. Deljanin,
Brank, Heated sapphires from around the world , ICA congress,
Sydney, April 30 - May 3 2001 |
| 2. Coldham,
Terry, Australian sapphire "Foundation stone of Thai
Gemstone industry” , ICA Congress Sydney. |
| 3. Statistics of
sapphires cut but not set for jewelry delivered by ICA at
ICA Congress Sydney. |
|
