An unusual diamond
An inner core of river clear (as the old names used to put it) gem carbon was overgrown by a second layer containing millions of microscopic fluid inclusions. Much like similar ones in white milky quartz pebbles, the myriad reflections off all these inclusions add up to make the stone seem white and opaque. The crystal is a twinned one known as a macle.
Image credit: Anetta Banas