Marienglas, very clear selenite crystals from Brazil in matrix

A large specimen with very clear selenite crystals, popularly known as Maria Glass, embedded in a matrix of dark sedimentary rock. The water-clear to slightly striated crystal plates have grown in several generations one on top of the other. A phenomenon typical of the slow evaporation of saline solutions.

Selenite is the crystalline form of gypsum (CaSO₄·2H₂O), a calcium sulfate dihydrate. The two water molecules in the crystal lattice explain its most important characteristic: selenite is water-soluble. Prolonged contact with water corrosively dissolves the crystal plates. Cleaning must be done completely dry.

The historical name Maria Glass dates back to the Middle Ages. At that time, the transparent cleavage planes of selenite were used as a glass substitute for reliquaries of Mary. A chapter in mineralogy that is almost forgotten today.

The Brazilian deposit in Rio Grande do Sul, Iraí region, yields particularly clear Maria Glass crystals. The cleavage planes refract light like glass panes. Such pieces of this size are rare in commerce.

A piece with didactic depth and visual clarity, suitable for collectors documenting the spectrum of sulfate minerals.