Figure 15 shows the reduced density dependence of the Al-O coordination number n_{Al}^{O} = 4f_{Al(IV)}+5f_{Al(V)}+6f_{Al(VI)} versus its contributions from the four- plus five-coordinated species, 4f_{Al(IV)}+5f_{Al(V)}, and from the six-coordinated species, 6f_{Al(VI)}.