def calc_gamma_FeO_silicate(silicate_comp):
	"""
	Returns a value for gammaFeO in the silicate. Parameterization is based on Holdzheid,
	where gammaFeO is taken as a constant value from 1.7-3, dependent only upon MgO content. 

	Parameters
	----------
	silicate_comp: dict
		Dictionary of the composition of the silicate in wt% oxides.

	Returns
	-------
	float
		gammaFeO in the silicate melt
	"""

	if silicate_comp['MgO'] <= 20:
		return 1.7
	else:
		gamma_value =  1.7 + 0.1*(silicate_comp['MgO']-20)
		if gamma_value <= 3:
			return gamma_value
		else:
			return 3