Assignment 14 - Fancy Sapphire and Phenomenal Corundum Flashcards
What is padparadscha?
Padparadscha sapphire color is
an intensely saturated combination of pink and orange hues without any noticeable brown coloring.
How do the markets for pink and purple sapphires differ?
Pink and purple sapphires occupy different positions in the colored stone market.
Fine pink sapphires regularly command top prices, sometimes
comparable to padparadschas. Highly saturated pinks are rare, prized hues that sell quickly.
The market for purple sapphire is not as strong. This is partly because amethyst, an attractive purple gem, is readily available and relatively inexpensive.
What market factors affect the demand for yellow and orange sapphire?
The market for yellow and orange sapphires fluctuates with changes in fashions. Natural yellows from Sri Lanka are often in demand, along with basaltic material from Australia, Montana, and Southeast Asia. Yellow sapphires are also highly coveted in Thailand, as this color is associated with the country’s royalty. The Thais also value golden sapphires, which range from orangy yellow to yellowish orange with strong depth of color.
What is the most important factor affecting a color-change sapphire’s value?
The strength of the stone’s color
change is the most important quality factor affecting its value, followed in importance by bodycolor.
What causes the star in star corundum?
Asterism is caused by reflections from tiny, needle-like inclusions that are oriented in several specific directions.
Which star corundum bodycolors are the most valuable?
The most valuable star corundum has bodycolor that provides a strong contrast to the star.
Star ruby is typically the most valuable star corundum.
What country produces the finest fancy sapphires?
Sri Lanka produces what some consider the widest range of fancy sapphire colors in the world.
Madagascar is a major source of high-quality pink sapphire.
Where are the world’s most prolific corundum deposits?
Many prolific gem deposits lie within the geologic zone that runs from Mozambique in the south, through Tanzania, Kenya, and Ethiopia, to the Sudan in the north. This stretch, which includes Tanzania’s Umba River Valley, is considered one of the richest gem-bearing regions in the world.
The corundum is typically found in secondary deposits that erode
from their host rocks and concentrate in pockets and depressions in the river bottoms.
How does heat treatment improve the marketability of pink and yellow sapphires?
Purple sapphires are often heat-treated to achieve a more valuable pink or red hue.
Heating can brighten the hues of yellow and orange sapphires and
increase their saturation.
How did the controversy about beryllium lattice diffusion affect the corundum market?
The controversy devastated the fancy sapphire market. Traders refused to buy goods, and prices collapsed.
What processes do manufacturers use to synthesize fancy sapphire?
Because flame fusion—also known as the Verneuil method—requires less time and money than other methods, many synthetic fancy sapphires on the market are created by that process.
Some less-common corundum synthesis methods are pulling, flux, floating zone, and hydrothermal.
What are some modern non-gem uses for synthetic sapphire?
While synthetic ruby has been used in lasers for decades, a newer laser crystal is made of titanium-containing synthetic sapphire, grown by the pulling or freezing methods. These lasers can produce extremely short,
high-energy pulses, making them useful for a variety of research projects requiring precision.
Other applications being developed for synthetic corundum include highly energy-efficient circuitry and LEDs and scratch-resistant display screens, fingerprint scanners, and touchscreens for smartphones.
What materials are used to imitate fancy sapphire and star corundum?
Glass is the most common fancy sapphire imitation material. Corundum doublets also mimic fancy sapphire and star corundum. To imitate a star,
manufacturers sometimes adhere a piece of foil with engraved lines on it to the back of a corundum cabochon, causing a star to shine through the top of the cabochon dome. Cubic zirconia (CZ) can be produced in a wide variety of colors to act as an inexpensive fancy sapphire substitute.
What causes the pink color of corundum?
A. Iron
B. Copper
C. Chromium
D. Manganese
C.
Chromium
A major source of black star sapphire is
A. Thailand.
B. Tanzania.
C. Myanmar.
D. Sri Lanka.
A. Thailand.
