Friday, December 24, 2010

Blue and Rose Quartz: Nature's Special Colors

Quartz (SiO2) is a very common mineral and is found in all three classes of rocks (igneous, metamorphic, and sedimentary), in a variety of environments, and in a range of colors—including blue and pink. These two pleasing colors make these quartz specimens an important addition to a collector’s cabinet. Blue quartz is scarce while, on the other hand, rose quartz is more common. Rose quartz has a pale pink to rose red color. The color is thought to be caused by trace amounts of titanium. When samples of rose quartz from several localities were dissolved in acid, insoluble residues within the quartz were found. The residue was composed of thin microscopic fibers. These fibers may also be responsible for the color of rose quartz.

Well-formed crystals are rarely found—a true geological mystery. Most of these rare rose quartz crystals are from Minas Gerais, Brazil. Rose quartz is generally found in massive chucks associated with pegmatites (figure 1). The term pegmatite refers to the texture of certain coarse-grained crystalline granites. Since rose quartz is cloudy, it is not popular as a faceted gem but is commonly cut into cabochons (figure 2), rounded into beads for necklaces, or carved.

Figure 1. This large rose quartz specimen was found at the Devil's Hole Mine, about a mile from the town of Cotopaxi,  Colorado. Photo date 2007, © by A. Schaak.
 

Figure 2. A cabochon pendant from the same rose quartz boulder in figure 1. Photo date 2007,© by A. Schaak.
Rose quartz is the state mineral of South Dakota. Some rose quartz from South Dakota contains microscopic rutile needles which produces a distinctive asterism or a star-shaped figure of light on the surface of polished pieces. There are several good occurrences of rose quartz in Fremont County, Colorado.

Blue quartz gets it deep to sky blue color from inclusions that scatter sunlight from inclusions. These inclusions could be tiny mineral grains of: ilmenite, rutile, tourmaline, crocidolite, magnesioriebeckite, or zoisite (maybe others). Inclusions selectively scatter visible light of the shorter, blue wavelength. Blue quartz has opalescence (waxy luster), chatoyancy (alternating luster), and asterism (presence of star-like figures).

Figure 3. These blue quartz megacrystals are located in the pegmatites of the Cape Ann Granite at Andrew’s Point in Rockport, Massachusetts. Photo date 2007, © by H. Renyck.
Blue quartz occurs at a number of localities. Colorado has an occurrence of blue quartz in Park County. Small, doubly terminated crystals in a rhyolitic porphyry, informally known as Llanoite, occurs in Llano County Texas. The blue crystals weather out and can be easily collected. Blue quartz is found in Wisconsin in a diorite near the Dairyland Power Dam near the town of Tony. Recently discovered blue quartz in the Cushing Point formation of Peak’s Island, Maine has inclusions that have the chemistry of biotite. The presence of biotite in blue quartz is new—past research has not listed biotite as a possible inclusion. Research suggests that the inclusion of biotite on Peak’s Island blue quartz may be responsible for giving this quartz its blue color. Blue quartz is also located in the pegmatites of the Cape Ann granite at Andrew’s Point in Rockport, Massachusetts (figure 4).
Figure 4. Close up view of blue quartz in Cape Ann Granite at Andrew’s Point in Rockport, Massachusetts. Photo date 2007, © by H. Renyck.
References:

Coblieg, T., 1986. Why is Blue Quartz Blue?, Geological Society of America 18: 567.

Frondel, C., 1962. The System of Mineralogy, 7th edition, vol. 3, Silica Minerals, John Wiley and Sons Publishers, N.Y., 334 p.

Koivula, j., 2003,. Blue Quartz. Gems & Gemology 39, p. 44-45.

Romero Silva, J.C. 1996. Blue Quartz from the Atequera-Olvera Ophite, Malaga, Spain. The Mineralogical Record 27, p. 99-103.

Rossman, G. R., 1994. Colored Varieties of the Silica Minerals: in Silica: Physical Behavior, Geochemistry and Materials Applications, edited by P.J. Heaney, C.T. Prewitt, and G. V. Gibbs, Washington, D.C., Mineralogical Society of America, Reviews in Mineralogy, vol. 29, p. 433-468.

Wise, M. A., 1981. Blue Quartz in Virginia, Virginia Minerals 27, p. 9-13.

Zolensky, M. E., Sylvester, P.J., and Paces, J. B., 1988. Origin and significance of blue coloration in quartz from Llano rhyolite (Illanite), north-central Llano County, Texas. American Mineralogist, 73, p. 313-232.













2 comments:

  1. Quartz crystals are an excellent way to take healing upon oneself. Crystal healing uses specific crystals to bring about healing and positive changes in the mind and body. The idea behind crystal healing is that gemstones carry vibrational rates, which can change a the vibrational rates of a person's aura.

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  2. Blue quartz is also prevalent in the Blue Ridge Mountains of Virginia, down through NC. My yard and neighboring creek are full of it. What's interesting is that it is usually in the form of a quartzite, "glued" together with an off-white chalky substance...I've been trying to find out what that is, because also occurring with this substance (in our creek) are tiny gold flakes, maybe schist or mica (seem to be too tiny for pyrite, which is also around us). Does anyone know what those minerals might be? Has anyone found this combination of minerals before?

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