This is an eye catching, multiple layered "sandwich" selenite specimen collected from the Lubin Mine in Lower Silesian Voivodeship, Poland. The specimen is 21 x 32 x 35 mm and weiight is 11 grams, in other words quite small.
Selenite is a variety of gypsum, a soft sulfate mineral that is composed of calcium sulfate dihydrate (CaSO4 · H2O). When chemically pure, gypsum is transparent and colorless, however, impurities give the gypsum a diverse range of colors and formations.
This selenite is uniqe in the way that it consists of two layers, one dark green and one light green selenite. The photos are taken in strong light, in normal daylight the colors will not be quite as intense. I do not have information about when it was found.