This remarkable rock occurs as a marginal phase of the granulitic albite granites which are found between Noqui and kilometre 16 on the road to San Salvador. In the hand-specimen it shows a finegrained slightly foliated structure with a characteristic pepper and salt appearance, due to the sprinkling of lustrous black plates of riebeckite among iron-stained granular crystals of quartz and felspar. A few small porphyritic crystals of orthoclase are embedded in the main mass of the rock, making up approximately 15 per cent of the whole.