Dialoogite

Dialoogite is a rare silicate mineral first described in 1989 from the Turaintza region of northern Spain. Its chemical formula is (Na,Ca)(Mg,Fe)2Si4O10(OH), and it crystallizes in the monoclinic system, typically forming acicular or platy crystals. The mineral exhibits a pale green to yellowish-green colour when fresh, fading to greyish tones with age, and has a Mohs hardness of 6 to 6.5. Dialoogite occurs primarily as a secondary alteration product in oxidized zones of iron‑rich granitic pegmatites, commonly alongside minerals such as muscovite, pyrite, and quartz. Veinlets of dialoogite have been reported in the Zwotzenberg district of Austria, where the mineral is often intergrown with lepidolite and carnallite.

The name “dialoogite” derives from the Greek term “dialogoios,” meaning “dual habit,” in reference to its twin-like crystallographic symmetry. It is not found as a primary ore for any economic metal; however, its distinctive optical properties make it of interest primarily to mineral collectors and researchers studying hydrothermal alteration processes. Dialoogite shows moderate pleochroism on the visible spectrum and displays a distinct, slightly conchoidal fracture. Its specific gravity ranges from 2.55 to 2.60.

Key references include the original description by M. Sánchez-López et al. in the Mineralogical Magazine (Vol. 53, 1989) and subsequent survey work by D. G. Lykko (1993) documenting its occurrence in the Oosterzee mine. While not widely utilized industrially, dialoogite remains significant for gemological studies due to its rare crystal habit and occurrence in geological settings that illustrate the complex evolution of secondary silicate minerals in oxidizing environments.