Corundum, Al2O3 (Aluminium Oxide),  is one of the simplest minerals in terms of chemical composition and crystal structure, yet produces two of the worlds most beautiful gemstones Ruby and Sapphire. The former is coloured red by the presence of Chromium ions as an impurity, whilst Sapphire is turned blue by the presence of Iron and Titanium. Both varieties are relatively common in the Earth's crust due to both aluminium and oxygen being ubiquitous elements, but good quality clear crystals are exceedingly rare, hence their precious stone status.

Description: This is a single, large, hexagonal ruby crystal, with an excellent termination on both sides. Only the top termination is the typical ruby-red. The sides and bottom termination are covered by a thin crust of original matrix material which has not been removed, but could be if desired. The ruby is quite gemmy and shows a degree of transparency. The whole specimen could be cut and polished to prduce a nice gem. However, left alone, this is a beautiul example of this colourful mineral.

Location: Maswingo, Zimbabwe.