Blue Quartz

 

last modified: Tuesday, 12-Apr-2011 19:16:43 CEST

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Blue  quartz is simply macrocrystalline quartz that is blue. The term is used for - at least - three different types of quartz:

So far no quartz that is blue because of color centers, similar to those found in amethyst or smoky quartz, has been found in nature. Amethyst from certain mines in Brazil will partially or completely turn blue on special treatment.

Some would say that the term "blue quartz" is reserved for rock crystal that appears blue by Rayleigh scattering. This, however, is the rarest form of blue quartz, and there is also a common denominator between all three forms: the color is caused by inclusions of other minerals, and not by built-in trace elements and/or lattice defects, like in amethyst, for example.

Because of this rather open definition, the specimen in the two images to the right both qualify as blue quartz.
The first image shows a rock crystal that is colored by tiny fibers, probably riebeckite from Minas Gerais, Brazil. In the "Locations and Specimen" section you will find another image of this crystal.

The second image shows another type, a massive macrocrystalline quartzite specimen of unknown origin, colored blue by some unknown embedded mineral, possibly dumortierite.

 

Specific Properties

The color can vary from gray to deep blue. Natural blue quartz is always colored by inclusions of other minerals, not by trace elements or color centers, so it is never transparent, just translucent.

 

Occurrence

This depends on the type of inclusion: Quartz that includes riebeckite occurs in metamorphic rocks, while inclusions of blue turmaline have been found in crystals from igneous rocks and pegmatites.

Grains of blue quartz are occasionally found as a constituent of igneous rocks.



 

Locations and Specimen

Brazil


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A  double terminated quartz crystal deeply colored blue by inclusions of fine needles of indigolite, a tourmaline. In the large versions of the image one can see that the needles are oriented randomly in the crystal. From the Jenipapo Mine, Itanga, Minas Gerais, Brazil.


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Another  blue quartz specimen, also from the Jenipapo Mine, Itanga, Minas Gerais, Brazil. Its color is much lighter and more uneven, in part because of additional cloudy white inclusions.



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This  image shows the same specimen as the first image on top of this page from a different perspective. One can see bundles of blue-gray fibers (probably riebeckite) that run roughly parallel to the c-axis. From an unknown location in Minas Gerais, Brazil.


Spain


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Antequera  near Malaga is a famous location for translucent quartz crystals of intense blue color. The cause of the color are fibrous inclusions of magnesio-riebeckite. The crystals often lack prism faces (m-faces) and are distorted, sometimes showing a strange surface pattern. The crystals can be found in narrow fissures in the metamorphic rock. Large, well-formed crystals are rare.

A locality with very similar looking crystals is Olvera near Cádiz, Andalusia. However, the crystals at that locality are colored by inclusions of the mineral aerinite (Romero Silva, 1997). Specimen with inclusions of both aerinite and magnesio-riebeckite have been observed, as well (Hyrsl & Niedermayr, 2003)

The two images show views of the same specimen from Olvera. One side has light blue, but larger crystals. The dark shiny crystals in the appeared when I dissolved a cover of carbonate cement.

Another nice image of this type of blue quartz can be found at the blue quartz description at mindat.org.



 

Further Information, Literature, Links



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