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A dioritic rock intergrown with chrysocolla is often missleadingly offered as "African turquoise".

Foto: K. Sieber, www.makrogalerie.de

 

The finely spread, powdery mineral that gives this rock a blue-green color was offered as »African Turquoise«. As we had our doubts, X-ray diffraction (EDX)  analyses have been done to determine the mineral content and the type of rock.

 

On the basis of the X-ray diffraction the components chlorite, kaolinite, muscovite (illite), quartz, anorthite or albite and possibly epidote and an amphibole could be identified. This mineral composition is typical for a decomposed granitic rock. The results do not provide any information about the identity of the coloring blue-green mineral. Additional thin section analysis clarified the situation.

Thin section analysis showed the mineralogical pattern und indications for a decomposed quartz-diorite in which chrysocolla has been formed mainly along fissures and crevices.

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Artifical product "Andara Crystal" (bottle glass)

Foto: K. Sieber, www.makrogalerie.de

 

The term "Crystal" is used for both: natural grown crystals as well as artificial glass. The use of the term "crystal" for not crystalised products is kind of missleading and prohibited in European countries.

Companys like Swarovski make use of this misleading linguistic extensively. For marketing reasons, Swarovski avoids the word "glass" whenever possible and rather speaks of »Swarovski Crystal«. However, especially when dealing with jewelry this creates a considerable risk of mistaking them for natural products. That is why the practice of Swarovski and other artificial glass produducers is to be refrained from.

The risk for mistaking artificial glass for a natural product multiplies significantly in the case of Andara Crystal by selling raw and tumbled stones "from natural deposits". The producers provide pictures of raw stones of several foot in diameter on the Internet with the intent of suggesting natural occurency.

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Vapor-coated quartz and topaze are becoming increasingly widespread in the jewelry sector

Foto: K. Sieber, www.makrogalerie.de

 

They have creativ sounding fantasy names such as "Angel Aura", "Aqua Aura" or "Tanzan Aura Quartz": gemstones with metallic coatings are spreading more and more in the form of cut jewelry and as treated raw crystals.

The process by which the crystals are coated is called "plasma sputtering" and works like a firing chamber in which a 2000°C hot plasma is generated. In this process, a metal vaporizes from an electrode that acts as a cathode. In the plasma, the metal is broken down into its atomic components and then deposited on all objects that are in the vicinity as an anode.

Originally, the process was developed to give any material new electrical and optical properties. However, as early as the 1970s it was discovered that the method was appropriate to create artificial color varieties of quartz and topaz for the jewellery market. As a result, some previously unknown color varieties came on the market (e.g. "Mystic Fire Topaz") beside many already known varieties like Citrine, Amethyst, Gold Topaz etc.

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The term "Ye Ming Zhu" is used (in a manner similar to that of the term "Jade") not for a single mineral, but for a whole range of different minerals and artificial products.  Their special feature is, that they show the special optical property of phosphorescence when exposed to daylight.

 

Ye Ming Zhu

Ye Ming Zhu - a phosphorescent ceramic (artificial product)

Foto: K. Sieber, www.makrogalerie.de

The list of natural minerals showing phosphorescence under rare circumstances is long: apatite, calcite, celestine, diamond and fluorite belong to it as well as garnet, magnesite, opal, spinel, spodumene and zircon. However, these minerals only phosphoresce if they contain certain impurities. As less than 1% copper (Cu) or silver (Ag) in Sphalerite (zinc blende, zinc sulphide), generates a yellowish-green glow. If it is contaminated (doped) with europium (an element of the Rare Earths group), it achieves a significantly longer (and brighter) phosphorescence time.

Alkaline Earth Aluminates contaminated with Rare Earth elements can develop phosphoresce for seconds to minutes. Especially the Rare Earth elements: Lanthanum (La), Europium (Eu) and Dysprosium (Dy) are able to interact with elements of the host mineral - e.g. Calcium (Ca), Strontium (Sr), Barium (Ba) and Aluminium (Al). They store the energy of the light, which is released with a certain delay as a visible glow.

According to the research of the EPI laboratory, several types of "Ye Ming Zhu" are offered on the Internet:

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This green rock is sold under the deceptive trade names »African Jade« or »Malachite Jade«.

Gemological examinations of the EPI-Lab showed that the physical properties of the stone differ significantly from those of the recognized Jade minerals jadeite and nephrite. The microscope revealed a granular rock consisting of dark to light green as well as colorless minerals. To rule out that this stone contains Jade minerals in minor quantities, Raman spectroscopy, EDX and thin section analysis we performed.

We found a lot of colorless quartz which is the main constituent of this stone. Two green minerals could be identified: light green diopside and a dark green mineral of the amphibole group. The black banding originates in the presence of ores like pyrite and goethite. The latter was probably formed by the conversion from hematite or magnetite.

Conclusion:

This stone has nothing to do with the known Jade minerals jadeite or nephrite. It is a green member of the quartzite rock group. The correct name is: Diopside-Quartzite.

Detailed information on this stone is available in our Archive (in german language).