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Yellow sapphire: description, properties and photos

Yellow sapphire

Yellow sapphire is one of the most popular transparent varieties of gem-quality corundum mineral. The properties of the gemstone are the same as those of blue sapphire and ruby (apart of the color). The color palette is limited to golden hues: from light yellow, pastel yellowish to vivid yellow-orange. This color is mainly due to the admixture of iron. In terms of beauty, the stone can be compared to the tropical sun imprisoned in the crystal. Crystals can have both bipyramidal and barrel-shaped and prismatic appearance.

Yellow sapphire

The most common color of the stone is light yellow. However, it is not much appreciated. The most expensive and valuable shade is «Golden Yellow». The properties of yellow sapphires are such that they are inferior in hardness only to diamonds. This is an excellent quality for a gem, as you can be sure that with prolonged daily wear, the edges will not be scratched and the luster will not fade. Corundum is famous for its durability and practicality. In addition, stability is typical for its color.

Yellow sapphire crystal

Properties

Mineral:

corundum

Chemical formula:

Al2O3

Crystal Systems:

trigonal

Mohs scale hardness:

9

Optical character:

anisotropic

Cleavage:

very imperfect

Density:

4.00 g / cm3

Luster:

Vitreous

Refractive index:

1,762-1,770

Birefringence:

0.008-0.010

Dispersion:

0,018

Color:

yellow, yellowish orange

Location

The most valuable specimens of yellow sapphires are mined in the deposits of Sri Lanka, especially Ratnapura area is known, where golden sapphires are mined in alluvial deposits. There are crystals suitable for cutting among the samples obtained with bright colors and fairly large sizes. Findings of more than 100 carats of gem quality are also known. Yellow corundums are found in deposits of other countries: Burma, Thailand, Tanzania. However, compared with Ceylon sapphires, the recoverable crystals are much smaller and less attractive in color.

Yellow Sapphire origin

Interesting facts

  • The identification of unheated specimens was difficult due to the fact that small needle inclusions were visually taken as partially dissolved rutile, a sign of warming in blue sapphires. However, it turned out that these are boehmite inclusions characteristic of unheated yellow sapphires.
  • Many laboratories conduct studies on the stability of the color of yellow sapphires, as there have been observations that they can gain saturation from exposure to ultraviolet radiation, and then vice versa return to their original state.
  • The popularity of yellow sapphire is largely due to its similarity to fancy yellow diamonds.
  • Today some of the best yellow sapphires are mined in the deposits of the island of Ceylon.

History

Yellow sapphires have been used along with other varieties of corundum since antiquity, but they were less known compared to the blue and red varieties. In ancient Vedic astrology (Jyotish Aurveda), yellow sapphire is considered a Jupiterian stone and acts as a symbol of prosperity and wealth. During the colonization years of Asian countries, yellow sapphires became popular in Europe; they are found in collections of famous jewelry houses such as Bvlgari and Cartier. Today, this gem is gaining popularity and is increasingly used in exclusive jewelry.

Enhancement

Like other color varieties of corundum, yellow sapphires are of interest as an object for treatment. The most valuable are unheated, not subjected to any kind of enhancement, except cutting. The classic way to obtain a more saturated color in light-colored natural samples is the thermal effect (heat treatment). Such heating is considered acceptable for corundum and is diagnosed by laboratories in a number of ways. Another fairly common method is heat treatment, accompanied by diffusion of beryllium into the stone structure. In this case, in contrast to the diffusion of titanium oxide, coloring is carried out to the full depth of the sample. This refinement method is less acceptable, although the stones can be attractive and bright. Another improvement method is improvement of clarity by filling cracks in low-quality fractured corundum with lead glass, which affects their strength, durability and beauty. These are cheap stones, which can more likely be called composite material.

Yellow sapphire

Photo

various forms of yellow sapphire crystals

On the photo: various forms of yellow sapphire crystals. The place of extraction is Sri Lanka.

tensor crack around a mineral inclusion formed during heat treatment

Photo taken under a microscope: tensor crack around a mineral inclusion formed during heat treatment

a large sample of faceted gem-quality corundum of top Golden color

In the picture: a large sample of faceted gem-quality corundum of top Golden color

unique unheated samples of more than 30 carats each (Sri Lanka)

On the photo: unique unheated samples of more than 30 carats each (Sri Lanka)

Untreated gold sapphire in the process of making a ring.

Untreated gold sapphire in the process of making a ring.

Video

On the video: Yellow corundum 11.75 ct

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