October 2023 – Goethite

Johann Wolfgang von Goethe was also intensively engaged in scientific questions. His main interest was geology and mineralogy. Therefore, it is perhaps not surprising that there is a mineral named after him – our mineral of the month October. Goethite is a common mineral from the mineral class of “oxides and hydroxides” of black-brown to black or light yellow color due to weathering. However, the so-called streak color differs from this, because goethite has a yellow-brown streak color. The streak color refers to the color of the mineral powder, which is used as a simple identification method to distinguish between minerals that appear similar on the outside. To determine the streak color, the mineral is rubbed with some pressure over a mostly white hard porcelain tablet. Goethite, as in this case here, often develops needle and radial crystals.

FeOOH

Locality: Ilmenau, Thüringen

Size: 4x8x6 cm (HxLxW)

Weight: 245 g