Colemanite minerals in three different sizes (C-3 mm, C-75 µm and C-45 µm) were supplied from the Eti Mine Company. These minerals were used as initial materials. It is well known that nanosize materials have a lot of positive technical properties. Therefore, in this study, C-3 mm mineral was ground by a high-energy ball mill in order to obtain nanocrystallite sized colemanite. Afterwards, milled powder was passed through a sieve of 25 µm of a vibratory sieve shaker (C-25 µm). Elemental properties of initial materials and milled powder were investigated with an oxide compound test and an energy dispersive spectrometer (EDS). Their crystal structure properties were examined with an Xray diffractometer (XRD). Results of elemental property indicate that the materials were not pure colemanite compound and the amount of boron oxide did not change significantly at the end of milling process. Results of crystal structure property show that crystallite size of the colemanite mineral at the end of milling process was reduced to nanoscale with a value of 63.6 nm. The findings obtained from this study will be useful for future science and engineering studies with not only colemanite mineral but also other boron minerals