063 / 021 - color change; light yellowish Green; very slightly greyish / light reddish Orange; very slightly brownish.
Alternative name, occurrence category: Rare
Zultanite (Color Change Diaspore)
Color: color change from light greyish green to light brownish
Hardness: 6.5 - 7
Refractive index: 1.68 - 1.75
Density: 3.30 - 3.40
Chemical composition: a-AlO(OH)
Crystal structure: Orthorhombic
Considered to be a collector's stone, Turkish diaspore gems with a color change effect are sold under the commercial names of Zultanite or Csarite. Specimens over 10 ct are rare
Zultanite (Colour Change Diaspore)
About Colour Change Diaspore - History and Introduction
Colour change diaspore is an aluminum oxide hydroxide mineral, and it is one of three major mineral components of bauxite. Bauxite is an important ore of aluminum widely used for many industrial purposes. Gemstone quality diaspore is extremely rare, and as its descriptive name suggests, it has a unique ability to change colour when viewed under different lighting conditions. Only a few gem types are known to possess the ability to colour change, which also includes alexandrite (chrysoberyl), sapphire, andesine and garnet. On very rare occasion, some diaspore may exhibit chatoyancy (cat's eye) effects. This is referred to as cat's eye diaspore.
The intensity of colour shift in colour change diaspore is typically very faint in smaller stones, but with larger specimens, the colour change can be very pronounced. In addition to the ability to change colour, diaspore is also known to exhibit pleochroism. Pleochroism is the ability to display various colors depending on the viewing angle and it is completely separate from the ability to change colour. A single stone can appear violet-blue, light green or pink to dark-red, as a result of pleochroism.
Colour change diaspore is mined commercially from only one location in the world, the Anatolian Mountains of Mugla, Turkey. Diaspore was actually discovered in the Ural Mountains of Russia in 1801, but it wasn't faceted as a gemstone until the early 1980s and it has only recently been mined on a commercial level. When colour change diaspore was first introduced it was marketed as 'Zultanite', after the company that owned the mining rights to the Turkish mines. However, the brand name was very short-lived and the gemstone is now referred to mostly by its mineral name.
Colour change diaspore can be easily distinguished from other similar gemstones by the unique presence of pleochroism and its unmistakable colour change effect. The excellent hardness and durability of diaspore can also help distinguish colour change diaspore from any other similar materials. Diaspore also has a distinct pearly luster which is difficult to replicate. Additionally it has perfect cleavage like diamond and topaz, which is a distinguishing feature. Spodumene is often confused with diaspore, but it does not possess the rare optical properties of colour change diaspore.
Colour Change Diaspore Origin and Gemstone Sources
Colour change diaspore can be found in various locations around the world, but the only major commercial source is Mugla, Turkey. Other smaller, but notable deposits have been found in Russia's Ural Mountain region, at mainly the Saranovskii Mine in Sarany, as well as in South Africa's Wessels and N'Chwaning mines. Deposits of diaspore crystals were discovered at Chester, Massachusetts (USA), but these were not of major commercial value. Other notable sources include New Zealand, Brazil, Argentina, UK, China, Arizona and Pennsylvania (USA).
Buying Colour Change Diaspore and Determining Colour Change Diaspore Gemstone Value Back to Top
Colour Change Diaspore Colour
Colour change diaspore owes its color to manganese. Under natural or fluorescent light, most specimens appear light-olive or kiwi-green with flashes of yellow. Under incandescent lighting, the colour shifts to more of a champagne hue. When exposed to subdued lighting (candlelight), a light pinkish-orange to raspberry-red colour can be seen. Mixed lighting sources can result in color combinations. Colour change diaspore also exhibits pleochroism; a single stone can appear violet-blue, light-green or pink to dark-red, depending on the viewing angle.
Colour Change Diaspore Clarity and Luster
Colour change diaspore has an extremely attractive, vitreous to pearly luster. High quality specimens have excellent transparency, but inclusions are very common. Eye-clean specimens are extremely rare, especially in larger stones. Some diaspore occurs with translucent material, but top grade faceted stones are very clear and transparent.
Colour Change Diaspore Cut and Shape
Colour change diaspore is most often faceted into traditional shapes, such as oval facets and rectangular step cuts. Cat's eye diaspore, a rare chatoyant variety, is always cut en cabochon. Since gem quality diaspore is extremely rare, fancy shapes and calibrated gems demand very high premiums.
Colour Change Diaspore Treatment
Colour change diaspore is not known to be treated or enhanced in any way. It is one of the few gemstones that remains completely untreated throughout production, from the mine to the market.