  Unconventional superconductivity has long been believed to arise from a
lab-grown correlated electronic system. Here we report compelling evidence of
unconventional nodal superconductivity in a mineral superconductor \rhs. We
investigated the temperature-dependent London penetration depth
$\Delta\lambda(T)$ and disorder evolution of the critical temperature $T_c$ and
upper critical field $H_{c2}(T)$ in synthetic miassite \rhs. We found a
power-law behavior of $\Delta\lambda(T)\sim T^n$ with $n\approx 1.1$ at low
temperatures below $0.3T_c$ ($T_c$ = 5.4 K), which is consistent with the
presence of lines of the node in the superconducting gap of \rhs. The nodal
character of the superconducting state in \rhs~was supported by the observed
pairbreaking effect in $T_c$ and $H_{c2}(T)$ in samples with the controlled
disorder that was introduced by low-temperature electron irradiation. We
propose a nodal sign-changing superconducting gap in the $A_{1g}$ irreducible
representation, which preserves the cubic symmetry of the crystal and is in
excellent agreement with the superfluid density, $\lambda^2(0)/\lambda^2(T)$.
