Three type Blue Quartz gemstone

Blue quartz is a group blue variety of quartz.  This rather open definition is due to the fact that no blue quartz has been found in nature with unique cause of coloration, there are no blue color center in quartz lattice to produce blue color.  So it is fundamental different from Amethyst’s color formation which is produced by purple color center [1].  Thus blue quartz has several different types [2][3]:

Type I: Blue color of single crystals quartz is due to Rayleigh scattering effect.  The Rayleigh scattering is the scattering of light by particles much smaller than the wavelength of the light.  It is the scattered light by small particles in the atmosphere that gives the blue sky. In blue quartz case, the light is scattered by abundant submicrometer-sized inclusions inside quartz crystal to cause sky blue color. The total amount of inclusions in the blue quartz is calculated to be 0.02 %. This is the rarest form of blue quartz, and this type of blue quartz exhibits a particularly beautiful blue coloration, which is sky blue in the center of each crystal and darker at the margins.  In addition, in certain orientations these crystals display an intense silver-blue chatoyant flash.

Type II: Blue color of single crystal quartz is due to evenly distributed inclusions of blue minerals, like magnesio-riebeckite or tourmaline. The blue color is caused by light reflection  of the included blue minerals, however the inclusions are individually too large (~0.1 x 1 x 20 μm) to contribute to the blue color by Rayleigh scattering.

Type III: Blue color of ploy-crystal quartz is due to inclusions of blue minerals, the inclusions of blue minerals have much larger size than the size of inclusions in type I and type II.  This type of blue quartz is similar to blue aventurine that is also colored by embedded blue minerals, like dumortierite. In general, blue quartz has less blue inclusions and shows light blue color with blue pattern.  Blue aventurine has more blue inclusions and shows evenly distributed dark blue color. There is no clear boundary between type III blue quartz and blue aventurine.

It is believed that Blue Quartz is a soothing and calming stone, bringing a relaxing, peaceful vibe to any situation. Like all crystal quartzes, the blue quartz has a hardness of 7 on the Mohs scale and is thus insensitive to scratches.

Blue quartz occurs at many localities in worldwide. In USA, One famous localities is in Llano County Texas where it is found as small doubly terminated crystals in a rhyolitic porphyry called, informally, llanoite. The crystals weather loose and can be collected easily. Blue quartz is found in Wisconsin, most notably in a diorite exposed by the Dairyland Power Dam near Tony.

High quality Blue Quartz (Type I and II) are usually faceted for ring and pendant centerpieces, and less quality Blue Quartz (Type III) is most often used in gemstone beads .

Reference:

[1] G.R. Rossman, “Colored varieties of the silica minerals”, Reviews in Mineralogy, Vol.29 

[2] Jayaraman, N. (1939). The cause of colour of the blue quartzes of the charnockites of South India and the Champion Gneiss and other related rocks of Mysore. In Proceedings of the Indian Academy of Sciences, Section A (Vol. 9, No. 3, pp. 265-285). Indian Academy of Sciences.

[3] Pacns, J. B. (1988). Origin and significance of blue coloration in quartz from Llano rhyolite (llanite), north-central Llano County, Texas. American Mineralogist, 73, 313-323.