Under a polarizing microscope, this mineral is characterized by first-order gray interference colors, low relief, and minimal twinning.
Under a polarizing microscope, this mineral is characterized by first-order gray interference colors, low relief, and minimal twinning. It lies at the top of a diamond-shaped compositional diagram whose other corners consist of alkaloid feldspar, plagioclase, and feldspathoid minerals. Like feldspar, it is a framework mineral. One form of this mineral, which usually has a trapezohedral trigonal system, displays deformed lamellae, and is found alongside coesite. That form of this mineral is only found near shatter cones, is produced by impact events, and is described as "shocked." Gem varieties of this piezoelectric mineral include onyx and amethyst. For 10 points, name this abundant mineral that defines a 7 on the Mohs scale, which is made of silicon dioxide.
Under a polarizing microscope, this mineral is characterized by first-order gray interference colors, low relief, and minimal twinning.
quartz [prompt on "silicon dioxide"; prompt on "silica"]