This is a Complete very rare Pseudocubic Quartz crystal in collectors box. The form is more correctly a skewed cube with overdeveloped rhombohedral faces that are not at 90 degrees but can look like it from several angles.
The color of these quartz crystals is, in large part at least, dependent upon the color of the gypsum deposits nearby. Those crystals occurring near the contact of the gypsum with the red shale are decidedly darker colored.
Height- 1.8 cm