Rhyolite with Blue Quartz ("Que Sera Stone")

Rhyolite with blue quartz phenocrysts #400 and #401
Locality: Brazil; exact locality unknown
Dimensions: [to be added]

Also known by the trade name "que sera stone", and frequently misidentified as llanite, another rhyolite with blue quartz. 

Many online rock and crystal sellers confuse que sera stone (Brazil) with llanite (Texas). In hand sample, they may appear somewhat similar unless they are side-by-side, and both are porphyritic rhyolites with blue quartz phenocrysts and pink feldspar. However, as is clear from these images, there are several discernable differences:

• The llanite groundmass is brown/tan and darker, while the que sera stone is gray/green, and lighter.
• The feldspar crystals in llanite are typically much smaller and less euhedral than those in the que sera stone in hand sample. My samples of que sera stone are fairly typical of what is on the market, however in polished/carved pieces sold online, larger, euhedral feldspar crystals are more common.
• Both of these differences are consistent across the sole public outcrop of llanite in central Texas; I cannot say if the Brazilian stone shows any variance.
• Llanite is documented only from two localities: Llano County, Texas, and reportedly one location in Africa*. By definition, this would be mean que sera stone and llanite are not the same rock.

Images of llanite (porphyritic rhyolite with blue quartz phenocrysts):

While the source of the blue coloration in the quartz of que sera stone is not currently known, in July of this year (2022) a preliminary study was published which compared the blue quartz-bearing volcanic rocks of Brazil with those of Texas. This preliminary study aims to lay the groundwork for further research in the processes that form blue quartz and the geological significance of those processes. The paper is free to download and can be found here: Blue quartz in Brazil: the Rio dos Remédios occurrence – preliminary study. 

For more information on llanite, please follow this link to the llanite post. [Link will be added when post is published.]

* R.M. Reed, a research geologist with the University of Texas is typically referenced for the African locality. Unfortunately, at the time of this post, the page published in 2007 as "Lllanite in Africa? Reeds Granite Page. The University of Texas at Austin. http://uts.cc.utexas.edu/~rmr/llanite2.html" has been taken down, so I have not been able to read the research myself.