Limonite after Marcasite
specimen number:
1052508
location:
Bytom, Silesian Voivodeship, Poland
description: A pseudomorph is a mineral that has replaced another mineral while keeping the original crystal shape. This process occurs when a precursor mineral becomes unstable in its environment and chemically changes into a new substance. In the case of limonite after marcasite, the original iron sulfide crystals are exposed to oxygen and water, often near the surface of the earth. Over time, the sulfur is removed and the iron is transformed into a mixture of iron oxides and hydroxides. Geologically, this is a common form of weathering in ore deposits and sedimentary rocks. The resulting specimen looks exactly like the original bladed or cockscomb marcasite crystal, but it is now composed of earthy brown or yellowish-brown limonite. These specimens are fascinating to researchers and collectors because they show a complete chemical transition while perfectly preserving the complex geometric form of the mineral that is no longer there.
Crystals of what were once marcasite to 0.5 cm in size, these now replaced by limonite, and scattered across the top of matrix. In good condition. The specimen comes with an antique label as shown at the end of the video and dates to the very early 20th century.
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