diff --git a/dsharp_opac/dsharp_opac.py b/dsharp_opac/dsharp_opac.py
index 9becb6a..6909b23 100755
--- a/dsharp_opac/dsharp_opac.py
+++ b/dsharp_opac/dsharp_opac.py
@@ -1423,7 +1423,8 @@ def nk(self, lam):
         k : float
         :    imaginary part of mixed optical property
         """
-        from mpmath import findroot
+        from scipy.optimize import newton
+
         l_arr = np.array(lam, ndmin=1)
         eps_mean = np.empty(np.shape(l_arr)).astype('complex')
 
@@ -1439,7 +1440,7 @@ def nk(self, lam):
                 #
                 def fct(x):
                     return sum(self.abundances * ((eps - x) / (eps + 2 * x)))
-                eps_mean[i] = complex(findroot(fct, complex(0.5, 0.5)))
+                eps_mean[i] = newton(fct, x0=(0.5 + 0.5j))
             elif self.rule.lower() == 'maxwell-garnett':
                 #
                 # kataoka et al. 2014, eq. 3
diff --git a/pyproject.toml b/pyproject.toml
index 6baa0ba..93bcbfc 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -20,9 +20,6 @@ dependencies = [
     "scipy>=1.13.0",
     "matplotlib>=3.8.0",
     "astropy>=7.0.0",
-
-    # only need mpmath.findroot, which I suspect scipy.optimize.fsolve can replace
-    "mpmath>=1.3.0",
 ]
 
 [project.urls]