diff --git a/docs/module_categories.json b/docs/module_categories.json
index 1391908cad..af20960047 100644
--- a/docs/module_categories.json
+++ b/docs/module_categories.json
@@ -34,7 +34,8 @@
             "m_acoustic_src",
             "m_body_forces",
             "m_pressure_relaxation",
-            "m_collisions"
+            "m_collisions",
+            "m_eos_mie_gruneisen"
         ]
     },
     {
diff --git a/src/common/m_eos_mie_gruneisen.fpp b/src/common/m_eos_mie_gruneisen.fpp
new file mode 100644
index 0000000000..24963c2cb8
--- /dev/null
+++ b/src/common/m_eos_mie_gruneisen.fpp
@@ -0,0 +1,102 @@
+!>
+!! @file m_eos_mie_gruneisen.fpp
+!! @brief Contains module m_eos_mie_gruneisen
+
+#:include 'macros.fpp'
+
+!> @brief Generic Mie-Gruneisen equation of state, p = p_ref(rho) + Gamma*rho*(e - e_ref(rho)) with constant Gamma, split into a
+!! reference-curve provider and a curve-agnostic assembler (Arienti et al., GALCIT FM99-8, 2004). Materials differ only in the
+!! provider: stiffened gas ships here and the JWL principal isentrope follows with its consumer. Leaf module; no solver path calls
+!! it yet.
+module m_eos_mie_gruneisen
+
+    use m_precision_select
+
+    implicit none
+
+    private
+    public :: s_mg_stiffened_reference, f_mg_pressure, f_mg_internal_energy, f_mg_dp_drho, f_mg_dp_de, f_mg_sound_speed_sq
+
+contains
+
+    !> Stiffened gas as a Mie-Gruneisen reference curve: Gamma = gamma_s - 1, p_ref = -pi_inf, e_ref = pi_inf/rho, plus the density
+    !! derivatives. Template for the JWL isentrope; ideal gas is the pi_inf = 0 sub-case.
+    pure subroutine s_mg_stiffened_reference(gamma_s, pi_inf, rho, gamma_mg, p_ref, dp_ref, e_ref, de_ref)
+
+        $:GPU_ROUTINE(parallelism='[seq]')
+
+        real(wp), intent(in)  :: gamma_s, pi_inf, rho
+        real(wp), intent(out) :: gamma_mg, p_ref, dp_ref, e_ref, de_ref
+
+        gamma_mg = gamma_s - 1._wp
+        p_ref = -pi_inf
+        dp_ref = 0._wp
+        e_ref = pi_inf/rho
+        de_ref = -pi_inf/rho**2
+
+    end subroutine s_mg_stiffened_reference
+
+    !> p = p_ref + Gamma*rho*(e - e_ref).
+    pure function f_mg_pressure(gamma_mg, rho, e_int, p_ref, e_ref) result(pres)
+
+        $:GPU_ROUTINE(parallelism='[seq]')
+
+        real(wp), intent(in) :: gamma_mg, rho, e_int, p_ref, e_ref
+        real(wp)             :: pres
+
+        pres = p_ref + gamma_mg*rho*(e_int - e_ref)
+
+    end function f_mg_pressure
+
+    !> Inverse of f_mg_pressure: e = e_ref + (p - p_ref)/(Gamma*rho).
+    pure function f_mg_internal_energy(gamma_mg, rho, pres, p_ref, e_ref) result(e_int)
+
+        $:GPU_ROUTINE(parallelism='[seq]')
+
+        real(wp), intent(in) :: gamma_mg, rho, pres, p_ref, e_ref
+        real(wp)             :: e_int
+
+        e_int = e_ref + (pres - p_ref)/(gamma_mg*rho)
+
+    end function f_mg_internal_energy
+
+    !> Thermodynamic derivative dp/drho at constant specific internal energy, in terms of pressure: dp_ref + (p - p_ref)/rho -
+    !! Gamma*rho*de_ref, where dp_ref and de_ref are the reference-curve density derivatives.
+    pure function f_mg_dp_drho(gamma_mg, rho, pres, p_ref, dp_ref, de_ref) result(dp_drho)
+
+        $:GPU_ROUTINE(parallelism='[seq]')
+
+        real(wp), intent(in) :: gamma_mg, rho, pres, p_ref, dp_ref, de_ref
+        real(wp)             :: dp_drho
+
+        dp_drho = dp_ref + (pres - p_ref)/rho - gamma_mg*rho*de_ref
+
+    end function f_mg_dp_drho
+
+    !> Thermodynamic derivative dp/de at constant density: Gamma*rho, the defining property of the Gruneisen coefficient.
+    pure function f_mg_dp_de(gamma_mg, rho) result(dp_de)
+
+        $:GPU_ROUTINE(parallelism='[seq]')
+
+        real(wp), intent(in) :: gamma_mg, rho
+        real(wp)             :: dp_de
+
+        dp_de = gamma_mg*rho
+
+    end function f_mg_dp_de
+
+    !> Squared sound speed, assembled from the exposed derivatives per the frozen identity c^2 = dp/drho|_e + (p/rho^2)*dp/de|_rho
+    !! (Arienti et al. 2004; Menikoff and Plohr 1989). Can be negative outside the admissible domain, so the caller tests it before
+    !! taking a square root.
+    pure function f_mg_sound_speed_sq(gamma_mg, rho, pres, p_ref, dp_ref, de_ref) result(c_sq)
+
+        $:GPU_ROUTINE(parallelism='[seq]')
+
+        real(wp), intent(in) :: gamma_mg, rho, pres, p_ref, dp_ref, de_ref
+        real(wp)             :: c_sq
+
+        c_sq = f_mg_dp_drho(gamma_mg, rho, pres, p_ref, dp_ref, de_ref) + pres/rho**2*f_mg_dp_de(gamma_mg, rho)
+
+    end function f_mg_sound_speed_sq
+
+end module m_eos_mie_gruneisen
diff --git a/toolchain/mfc/test_mg_eos.py b/toolchain/mfc/test_mg_eos.py
new file mode 100644
index 0000000000..a87521a90a
--- /dev/null
+++ b/toolchain/mfc/test_mg_eos.py
@@ -0,0 +1,134 @@
+"""Manufactured verification for src/common/m_eos_mie_gruneisen.fpp.
+
+The Mie-Gruneisen backend is not yet runtime-selectable, so it has no golden case; these
+tests mirror the Fortran formulas line for line and run in CI with the toolchain unit
+tests. They check exact reduction to stiffened gas, the analytic sound speed and
+thermodynamic derivatives against finite differences of the frozen identity, and the
+isentrope self-consistency of the reference curves (Arienti et al., GALCIT FM99-8, 2004;
+Menikoff and Plohr, Rev. Mod. Phys. 61, 75, 1989).
+"""
+
+from math import exp
+
+
+# Generic Mie-Gruneisen assembler, mirroring m_eos_mie_gruneisen.fpp
+def mg_pressure(gamma_mg, rho, e_int, p_ref, e_ref):
+    return p_ref + gamma_mg * rho * (e_int - e_ref)
+
+
+def mg_internal_energy(gamma_mg, rho, pres, p_ref, e_ref):
+    return e_ref + (pres - p_ref) / (gamma_mg * rho)
+
+
+def mg_dp_drho(gamma_mg, rho, pres, p_ref, dp_ref, de_ref):
+    return dp_ref + (pres - p_ref) / rho - gamma_mg * rho * de_ref
+
+
+def mg_dp_de(gamma_mg, rho):
+    return gamma_mg * rho
+
+
+def mg_sound_speed_sq(gamma_mg, rho, pres, p_ref, dp_ref, de_ref):
+    return mg_dp_drho(gamma_mg, rho, pres, p_ref, dp_ref, de_ref) + pres / rho**2 * mg_dp_de(gamma_mg, rho)
+
+
+def stiffened_reference(gamma_s, pi_inf, rho):
+    """Stiffened gas as a Mie-Gruneisen reference curve."""
+    return gamma_s - 1.0, -pi_inf, 0.0, pi_inf / rho, -pi_inf / rho**2
+
+
+def jwl_reference(rho, A, B, R1, R2, omega, rho0):
+    """Synthetic (non-calibrated) JWL-form principal isentrope, exercising a density
+    dependent reference curve."""
+    V = rho0 / rho
+    e1, e2 = A * exp(-R1 * V), B * exp(-R2 * V)
+    p_ref = e1 + e2
+    e_ref = e1 / (rho0 * R1) + e2 / (rho0 * R2)
+    dp_ref = (V / rho) * (R1 * e1 + R2 * e2)
+    de_ref = p_ref / rho**2
+    return omega, p_ref, dp_ref, e_ref, de_ref
+
+
+# ideal air, water (stiffened), a stiff solid, monatomic: (gamma_s, pi_inf, rho, e)
+SG_CASES = [
+    (1.4, 0.0, 1.2, 2.5e5),
+    (4.4, 6.0e8, 1000.0, 3.0e5),
+    (3.0, 1.0e5, 50.0, 2.0e4),
+    (1.667, 0.0, 0.1, 2.0e6),
+]
+
+JWL_PARAMS = (5.0e11, 8.0e9, 4.5, 1.2, 0.3, 1600.0)
+JWL_STATES = [(rho, e) for rho in (900.0, 1600.0, 2400.0) for e in (1.0e6, 4.0e6)]
+
+
+def rel(a, b):
+    return abs(a - b) / max(1.0, abs(b))
+
+
+def test_stiffened_gas_reduction():
+    """The generic assembler fed the stiffened reference curve must reproduce the
+    analytic stiffened-gas pressure, energy round-trip, and sound speed exactly."""
+    for gamma_s, pi_inf, rho, e in SG_CASES:
+        gamma_mg, p_ref, dp_ref, e_ref, de_ref = stiffened_reference(gamma_s, pi_inf, rho)
+        p_mg = mg_pressure(gamma_mg, rho, e, p_ref, e_ref)
+        assert rel(p_mg, (gamma_s - 1.0) * rho * e - gamma_s * pi_inf) < 1.0e-13
+        assert rel(mg_internal_energy(gamma_mg, rho, p_mg, p_ref, e_ref), e) < 1.0e-13
+        c2 = mg_sound_speed_sq(gamma_mg, rho, p_mg, p_ref, dp_ref, de_ref)
+        assert rel(c2, gamma_s * (p_mg + pi_inf) / rho) < 1.0e-13
+
+
+def test_derivatives_and_sound_speed_vs_finite_difference():
+    """Analytic dp/drho|_e, dp/de|_rho, and c^2 against central finite differences of
+    p(rho, e) for the density-dependent JWL-form reference curve."""
+    A, B, R1, R2, omega, rho0 = JWL_PARAMS
+
+    def p_of(r, en):
+        g, p_r, _, e_r, _ = jwl_reference(r, A, B, R1, R2, omega, rho0)
+        return mg_pressure(g, r, en, p_r, e_r)
+
+    for rho, e in JWL_STATES:
+        g, p_ref, dp_ref, e_ref, de_ref = jwl_reference(rho, A, B, R1, R2, omega, rho0)
+        pres = mg_pressure(g, rho, e, p_ref, e_ref)
+
+        h = rho * 1.0e-6
+        fd_dp_drho = (p_of(rho + h, e) - p_of(rho - h, e)) / (2.0 * h)
+        assert rel(mg_dp_drho(g, rho, pres, p_ref, dp_ref, de_ref), fd_dp_drho) < 1.0e-6
+
+        he = e * 1.0e-6
+        fd_dp_de = (p_of(rho, e + he) - p_of(rho, e - he)) / (2.0 * he)
+        assert rel(mg_dp_de(g, rho), fd_dp_de) < 1.0e-9
+
+        c2_fd = fd_dp_drho + (pres / rho**2) * mg_dp_de(g, rho)
+        assert rel(mg_sound_speed_sq(g, rho, pres, p_ref, dp_ref, de_ref), c2_fd) < 1.0e-6
+
+
+def test_isentrope_self_consistency():
+    """Both reference curves must satisfy de_ref/drho = p_ref/rho^2, the density form
+    of de = -p dv along an isentrope; this is what makes them valid MG references and
+    catches per-mass vs per-initial-volume scaling errors in e_ref."""
+    A, B, R1, R2, omega, rho0 = JWL_PARAMS
+    for rho in (900.0, 1600.0, 2400.0):
+        _, p_ref, _, e_ref, de_ref = jwl_reference(rho, A, B, R1, R2, omega, rho0)
+        assert rel(de_ref, p_ref / rho**2) < 1.0e-13
+        h = rho * 1.0e-6
+        _, _, _, e_hi, _ = jwl_reference(rho + h, A, B, R1, R2, omega, rho0)
+        _, _, _, e_lo, _ = jwl_reference(rho - h, A, B, R1, R2, omega, rho0)
+        assert rel((e_hi - e_lo) / (2.0 * h), de_ref) < 1.0e-6
+    for gamma_s, pi_inf, rho, _ in SG_CASES:
+        _, p_ref, _, _, de_ref = stiffened_reference(gamma_s, pi_inf, rho)
+        assert rel(de_ref, p_ref / rho**2) < 1.0e-13
+
+
+def test_admissibility_scan():
+    """c^2 > 0 over the synthetic envelope for both reference curves."""
+    A, B, R1, R2, omega, rho0 = JWL_PARAMS
+    for rho, e in JWL_STATES:
+        g, p_ref, dp_ref, e_ref, de_ref = jwl_reference(rho, A, B, R1, R2, omega, rho0)
+        pres = mg_pressure(g, rho, e, p_ref, e_ref)
+        assert mg_sound_speed_sq(g, rho, pres, p_ref, dp_ref, de_ref) > 0.0
+    for gamma_s, pi_inf, rho, e in SG_CASES:
+        g, p_ref, dp_ref, e_ref, de_ref = stiffened_reference(gamma_s, pi_inf, rho)
+        # admissible states carry thermal energy on top of the reference energy;
+        # below e_ref the stiffened gas is in tension past -pi_inf and c^2 < 0 is correct
+        pres = mg_pressure(g, rho, e_ref + e, p_ref, e_ref)
+        assert mg_sound_speed_sq(g, rho, pres, p_ref, dp_ref, de_ref) > 0.0