Fenster Quartz

It seems that I cannot resist the various forms of quartz (silicon dioxide). In my defense, quartz (silicon dioxide) is the most common mineral on Earth (think beach sand and sand dunes) and one of the most diverse minerals-- in terms of its physical characteristics. 

To date, I have previously posted the following four write-ups about quartz: 

May 31, 2026 “Rose Quartz”

August 26, 2016 “Varieties of Quartz, Part 1”

Sept 14, 2018 “Varieties of Quartz, Part 2 “

Sept 23, 2028 Black Onyx Quartz

This current blog concerns a rare form of quartz, called “Fenster quartz  = (SiO₂)

During its crystallization, the sunken faces of fenster quartz crystals are occasionally sheeted over by a thin layer of more quartz that traps whatever water or mud might have been around at the time of the formation of this mineral. As a result, the crystallizing material experienced complex, fluctuating geological conditions during formation, which caused its unique layered appearance. This type of crystal has a very complicated internal structure that looks very complicated. Europeans refer to this material as “Fenster Quartz,” which is derived from the German word “das Fenster,” meaning “the window.” Fenster quartz develops in pegamatitic veins where unstable growth (with inclusions) took place. It is not a unique mineral, but it is an unusual growth pattern for quartz. 

Furthermore, fenster quartz is a coupling of clear quartz and elestial quartz. The result is that a crystal has repeating faces, which remind some folks of “an infinite multi-verse of repeating opportunities and outcomes.” This form of quartz is also known as “window quartz.” Variations of this mineral range from rusty/smokey” (like the one shown here) to perfectly clear. It is an affordable mineral if you wish to add it to your collection.

 

Fenster quartz is found in Brazil (most common source), Madagasgar, Africa, and in USA (at the Herkimer Diamond site---see one of my previous posts concerning this locality).

Two views (front and back) of the same specimen of fenster quartz (eclestial quartz) is 40 mm wide, 40 mm long, and 30 mm thick at its thickest point. It was collected at Arramberri, Nuevo Leon, south of Monterrey, in northeastern Mexico.