gulkroppens

Gulkroppens is a hypothetical mineral species used in speculative geology and world-building to illustrate color-bearing minerals. It is described as a soft, opaque yellow mineral with a waxy to resinous luster and a Mohs hardness of about 2.5 to 3.5.

Gulkroppens forms in low-temperature hydrothermal veins and as late-stage crystallizations in porous sedimentary rocks, often coating surfaces with thin, tabular crystals. The color ranges from pale lemon to deep ochre, influenced by trace impurities such as iron and manganese oxides. It is commonly found with quartz, calcite, and goethite.

The name derives from the Swedish gulkropp, meaning the yellow body, chosen for its distinctive hue in the fictional setting of the Archipelago Realm. Notable outcrops are described near Drottvik and on Solö, where it is depicted as having historic pigment and glazing uses.

In fictional geology, gulkroppens serves to discuss pigment production, environmental ethics, and the interaction of mineral coloration with trace elements. It is sometimes compared to real yellow pigments such as cadmium yellows for pedagogical purposes.

See also: pigment minerals; hydrothermal ore deposits; fictional minerals in world-building.