Polycrystalline monazite (monoclinic LaPO4) was deformed by spherical indentation at room temperature. Slip systems were identified via transmission electron microscopy of thin sections prepared parallel and close to the indented surface. Dislocation Burgers vectors (b) were identified by Burgers circuit closure in high resolution transmission electron microscopic images, supplemented by diffraction contrast where possible. A total of 441 b determinations were made in 97 grains. The most common slip systems were [001]/(010), [100]/(010) and [010]/(100). Slip on (001) was less common. Many other less common slip systems and Burgers vectors were also identified, including b = [101], [101], [011], [110] and [111]. b = [101] dislocations dissociated into ½[101] partials, and b = [101] dislocations were deduced to dissociate into ½[101] partials, with a low energy stacking fault of ∼30mJ/m2. b = [100] dislocations could dissociate into 1/4[210] + 1/4[210] partials. b = [010] may sometimes dissociate into ½[010] + ½[010] partials. Other types of partial dislocations were also observed. All partial dislocations were climb-dissociated. The line energies of monazite dislocations and their partials were calculated, and stacking fault structures for partial dislocations were analyzed. Satisfaction of the Von Mises criterion for full ductility probably involved [101]/(111) and 〈011〉/{011} or {111} slip, but other combinations that required both b = [101] and 〈011〉 or 〈110〉 were possible. If deformation twinning was active, slip systems with b = 〈011〉 or 〈110〉 might not be necessary for full ductility.

Monazite (Monoclinic LaPO4) Slip Systems at Room Temperature. R.S.Hay: Philosophical Magazine, 2008, 88[36], 4243-70