  Persistent spin textures (PSTs) in momentum space have the potential to
enable spintronic devices which are currently limited by low spin lifetimes in
nonmagnetic spin-orbit coupled materials. We perform a first-principles study
on the proustite mineral family, Ag$_3$BQ$_3$} (B=As,\,Sb; Q=S,\,Se), and show
these chalcogenides exhibit a non-symmetry protected PST, which we refer to as
symmetry-assisted PSTs. Chemical substitution can be used to tune the PST
quality and properties, e.g., spin lifetime, and we find that a Rashba
anisotropy criterion correlates with the PST area and spin lifetime for two of
the three proustites examined. Last, we show that a first-order effective SOC
Hamiltonian, often used in two-dimensional systems, is insufficient to describe
the PST state in all proustites, suggesting that higher order models are
necessary to fully describe PSTs in bulk three-dimensional materials.
