Monday, 13 May 2013

Cordierite - Gems and Stone

Cleavage masses of cordieriteSilicate of aluminium and magnesium. Cordierite is named after French geologist P. Cordier. It is also known as dichroite, from the Greek two colored or iolite. From another Greek root, meaning violet the Vikings apparently knew how to use these navigational purposes. Because of its strong pleochroism behavior in relation to the incident light indicated the direction of the sun on overcast days. For this reason it has also been dubbed Vikings compass.

Crystal system

Orthorhombic

Appearance

Cordierite occurs as short multifaceted prismatic crystals. It is normally gray light violet. But can also be yellowish gray. It is not very lustrous but when transparent has vitreous luster transparent crystals display very strong pleochroism from blue gray to almost colorless or from violet to very pale grayish yellow. 

Physical properties


Cordierite 1.37ct TanzaniaIt has a hardness of 7-7.5 density varies between 2.53 and 2.65 9/ quality stones is usually between 2.57 and2.65gm/cm3 but for gem quality stones is usually between 2.57 and 2.61 g/cm3) the refractive indices are ca. nu 1.532. n71 times no 1.540, 071.549.


Genesis

It is found scattered in silica igneous rocks but mainly in larger crystals, in schist and areas of contact metamorphism.

Occurrence

It is found mainly in C: 1 Norway, Finland, Brazil, and Madagascar.

Gem quality cordierite has the same names) as the mineral itself. but was in they  as water sapphire. Particularly when the M if intense. This is perhaps its most familiar name in the trade
 

Appearance  

The color may vary from to violet blue, light blue or grayish blue N5’ very strong pleochroism, being a much ll 29; yellow in one direction. For obvious. Gems are cut so that this color is only A’ the most common type of cut is the react not always with truncated corners. One:-I cordierites with a cabochon cut or minutely particularly in the case of less transparent -w; 5‘numerous inclusions. Most stones are a few4 not too small, therefore, but never very
 

Distinctive features

An essential characteristic of cordierite is its exceptional pleochroisrn. Which may resemble certain tanzanites? Many cordierites cold. Grayish coloration, whereas’-g1; warmer color. Always with a hint of violet. Testing the density which is very different. Would remove any uncertainty
 

Occurrence

Cordierite comes mainly from the gem gravels of Sri Lanka, but also from the United Namibia.
 

Value

Rather low that of minor gemstones
 

Simulants and synthetic:

It is neither produced synthetically. 


Writer-Kennie Layman

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