Hollandite in Amethyst

Liviano Soprani

We are used to seeing groups of dark hollandite crystals that resemble sea urchins, but this time Mother Nature offered up a completely different and evocative vision. Crystals of hollandite, with the chemical formula Ba(Mn⁴⁺₆Mn³⁺₂)O₁₆, were observed inside a 15.00 ct amethyst cabochon. The arrangement of the acicular crystals created a shape resembling ears of barley (see above), making this photomicrograph look more like a botanical image. It was taken in darkfield illumination and oblique fiber-optic illumination with the use of image stacking. To obtain a good focus, the author took multiple photos on different focal planes and then used specific software to reconstruct the image—in this case, 67 stacked images.