Blue Quartz
 Blue and olive quartz from the Montezuma Mine in Minas Gerias, Brazil. Image courtesy of Dr. Rainer Schultz-Güttler There is little information available in literature regarding blue transparent quartz which has been derived from naturally occuring deposits. That is soon to change with an upcoming in-depth paper by Dr. Rainer Schultz-Güttler of the University of Sao Paulo, Mineralogical Institute in Brazil in which he will expand on an article he published in 2006. According to Dr. Schultz-Güttler, until relatively recently the only blue quartz currently known has been either the hydrothermally grown synthetic variety (colored by cobalt or treated iron-bearing) or that which owes its coloration to inclusions. In 2006, Dr. Schultz-Güttler reported that a new find at the Montezuma Mine in Minas Gerias, Brazil, yielded a small quantity of gem quality amethyst which, when treated, turns a beautiful blue color. This was accidently discovered when Montezuma material was gamma irradiated in an attempt to improve the green color achieved from heating amethyst. Simply put, amethyst greened by heating and then changed to blue by gamma irradiation and a second heating step. This stable color includes blues which are similar to those of tanzanite, iolite and sapphire and has been marketed as "blueberry quartz" (not to be confused with glass also sold as "blueberry quartz"). The pleochroic colors of the treated quartz were reported as strong violetish blue and reddish orange. He is preparing a much broader paper on the subject that is due for publication in Spring 2009 (personal communication, Schultz-Güttler, 2008). Occurances of material which will yield the blue color seem to be quite rare. For more information and images, see: Schultz-Güttler, R. and Kohigashi, H. C. (2006) Treated violetish blue to violet quartz from Brazil. Gems &Gemology, Vol. 42, No. 4, pp. 285-286.  Blue quartz from the Montezuma Mine in Minas Gerias, Brazil. My images of the crystal Don Hoover sent me did not do it justice; Dr. Rainer kindly provided this much better one which shows the range of shades obtainable. Image courtesy of Dr. Rainer Schultz-Güttler At the 2nd Annual European Gemmological Symposium held October 2008 in London, Dr. Ulrich Henn's presentation "Colour-enhanced Quartzes and their Identification - New Results on Green, Yellow-Green and Violet-Blue Quartzes from Brazil" included an overview of how blue color is obtained in transparent quartz. A few of my notes follow both from the portion concerning blue quartz, minus the chemistry for now, along with that from personal communication (please refer to his publications for more detail). After first defining "wet" quartz vs "dry" quartz, Dr. Henn discussed heating iron-bearing amethyst quartz 400 - 500 C to produce green ("prasiolite"), followed by gamma irradiation, then heat again to produce a blue violet shade which he also referred to as "safirita" quartz. The mechanism responsible for the blue color is still not fully understood. In contrast, when quartz from geodes in basaltic rocks were irradiated, colorless quartz turned a green that is attributed to NBO centers (dangling bonds) which are similar to defects in silica glass or ultra pure glassfiber material free of iron and alumina (personal communication, Schultz-Güttler, 2008: "that's the point, the NBO or NBOH does not need iron or alumina, like pegmatitic citrine (Al3+) or amethyst. It is therefore something special, although not very stable to UV light or heat."). In his overview of how blue is obtained, the starting material was treated amethyst resulting from gamma irradiated colorless or pale yellow material. Not all the resulting amethyst will produce a green which will be able to be treated to blue and furthermore, under the same heating conditions some becomes yellow (citrine). Dr. Henn also posed the question of how treatment and original material might be determined. He listed the following sources of green quartz (stability: Güttler, 2006):
"....two types of defects in quartz: general defects such as vacancies, substitutions and interstitial defects, and special defects related to chemical bonding and electron density. In vacancy defects, an atom is missing from the structure; in substitution defects, an atom of a different element replaces the silicon atom, and in interstitial defects, an atom of a different element is caught within the crystal lattice. He then brought up the concept of "wet" and "dry" quartz. "Dry" quartz is normally associated with pegmatitic origins, and contains no OH or Si-OH (silanol) groups, though it can contain aluminum or lithium substitutions. "Wet" quartz does contain OH and Si-OH groups, and is associated with the hydrothermal processes, such as those producing geodes. Depending on the defects present, heating amethystine (iron-bearing) quartz to the 400 - 500 degree Celcius range can produce either yellow to orange colours, or a green colour (prasiolite). Further heating and gamma irradiation of the prasiolite quartz can change it to a blue-violet colour, the so-called "blue-berry" quartz." Wight, Q. (2008) Centenary celebration for Gem-A. Canadian Gemmologist, 29 (4), pp. 135-141. (copies available at CGA: http://canadiangemmological.com/ecom/). When one searches the Internet for blue quartz or "blueberry" quartz, a limited amount of non-synthetic blue quartz is starting to be seen and its rarity is a major selling point. There is much more information about blue quartz colored by inclusions, including a section on the visually appealing and excellent reference site authored by Amir Akhavan: The Quartz Page. One does find a deluge of glass (some sold as quartz) as well as some synthetic blue quartz. It is tantalizing to think that someday a natural blue quartz might be pulled out of the ground at the Montezuma site, but in posing the possiblity to geophysicist Don Hoover, he replied: "As for whether any blue might come directly from the deposit, I would guess that it is not impossible, but that it is rather improbable, as you would need an initial irradiation event, a heating to green, and then another irradiation and heating." There are many publications dealing with color in natural and treated quartz both synthetic and natural, as well as information on other occurrences of natural green quartz and amethyst which may be "greened." Here are a selected few:
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