Published online by Cambridge University Press: 19 February 2020
We formulate a $q$-Schur algebra associated with an arbitrary
$W$-invariant finite set
$X_{\text{f}}$ of integral weights for a complex simple Lie algebra with Weyl group
$W$. We establish a
$q$-Schur duality between the
$q$-Schur algebra and Hecke algebra associated with
$W$. We then realize geometrically the
$q$-Schur algebra and duality and construct a canonical basis for the
$q$-Schur algebra with positivity. With suitable choices of
$X_{\text{f}}$ in classical types, we recover the
$q$-Schur algebras in the literature. Our
$q$-Schur algebras are closely related to the category
${\mathcal{O}}$, where the type
$G_{2}$ is studied in detail.