Vibrational spectroscopy of the borate mineral henmilite Ca2Cu[B(OH)4]2(OH)4

► Henmilite is a mineral with the potential to form polyborate nanomaterials. ► We have assessed the molecular structure of henmilite. ► Vibrational spectroscopy proves water is involved in the structure of the mineral. ► Hydrogen bond distances based upon the OH stretching vibrations using a Libowitzky equation were calculated.