The invention provides a method of manufacturing a solid phase barite containing material for use in a wellbore. The method includes the steps of providing the barite 5 containing material having relatively small particles with a particle size distribution of at least 50vol% particles having a diameter in the range of 1 .m to 1 O .m and at least 90vol% particles having a diameter in the range of 4 .im to 20 m; and contacting the barite containing material with a liquid in order to form relatively large particles having a particle size distribution with at least 90vol% of the particles having a diameter of at io least 30 m. There is also described a method of treating a wellbore with a fluid including the barite containing material. 63611741 (GHMatters) P94292.AU.1 JINGT 2/04/15 Particle Size Distribution 00I 01CO10 1000 3000 Particl Size ipm-) FigI
