gems-inclusions

Spectacular sample of complex color zoning in sphalerite.
What we see here is an advancing growth of twinned sphalerite crystal, where in some stages the crystal traps tiny solid inclusions, forming growth zones marked by small black particles when observed in transmitted light (probably galena or chalcopyrite inclusions). On the other hand, several colored zones (vertical on the picture) related to polysynthetic twinning of sphalerite are also present. They form as growth sectors, corresponding to different crystal faces present on the same growth front of this twinned crystal, which trap variable quantities of chromophore elements, with the result that some growth sectors have more color concentration than others.