Blocky Particles

Im starting to experiment with basic sfx creation but ive noticed that my particles are little squares rather than shapes? What am i doing wrong, ive used what i think are suitable ingame textures, My filter mode is additive so the alpha should be phased out?

Perhaps the texture you are using does not support additive and uses blend instead?

or it is a 8X8 texture he tries to use as 1X1, or vice versa.