... In the area of Namaacha, 50 km west of Maputo on the border with Swaziland there are formations of agate in acidic Volcanics. Agates in a size up to several decimeters can be found in the superficial closed Perlite rock. They show often bluish, brownish and yellowish colors with good contrast with the reddish brown matrix. Larger agates have often much macrocristallinic quartz in the center and are usually cracked..."

according to personal communicatrion with  Jens Götze, Freiberg