Current SiC-based ceramic-matrix composites (SiC-SiC CMCs) rely on carbon or boron nitride fiber-matrix interphases for toughness and flaw tolerance. However, oxidation of these interphases can be performance limiting in many CMC applications. The gamma-polymorph of the rare-earth disilicates (RE(2)Si(2)O(7)) is a potential oxidation-resistant alternative to carbon or BN. The formation of gamma-Y(2)Si(2)O(7) and gamma-Ho(2)Si(2)O(7) at different temperatures and processing environments was investigated. Silica-yttrium hydroxide and silica-holmium hydroxide dispersions were made and heat treated at 1200 degrees-1400 degrees C for 8 h in air and argon. LiNO(3) was added to the dispersions to enhance the formation of gamma-Y(2)Si(2)O(7) and gamma-Ho(2)Si(2)O(7). The effects of excess silica and LiNO(3) dopant on the formation of gamma-Y(2)Si(2)O(7) were investigated. Coatings of Y(2)Si(2)O(7) and Ho(2)Si(2)O(7) were made on alpha-SiC plate and SCS-0 SiC fiber using these dispersions. These were heat treated in argon and argon-500 ppm oxygen mixtures at 1400 degrees C/8 h. For coatings heat treated in argon-500 ppm oxygen mixtures, X-ray diffraction showed the formation of single phase gamma-Ho(2)Si(2)O(7) and a mixture of gamma and beta-Y(2)Si(2)O(7) at 1400 degrees C. Scanning electron microscopic image analysis gave an estimate of 18 vol% of excess silica for gamma-Y(2)Si(2)O(7) formed with high Si:Y ratio and similar to 5 vol% excess silica for material formed with lower Si:Y ratio. Transmission electron microscopy of samples directly beneath indentations showed both extensive dislocation slip and fracture.