The melting phenomena of the mixed crystal series åkermanite - sodium-gehlenite and gehlenite - sodium-gehlenite are given. The lower breakdown relations of this system are principally the same as those of the system åkermanite -gehlenite but the presence of an exsolution area modify the picture somewhat. The åkermanite breakdown relations of Harker and Tuttle (1956) are revised. The decomposition products of åkermanite at 6 kbar water pressure are hydrovesuvianite and clinopyroxene.
On sub solidus relations of silicates. IV. The systems åkermanite - sodium-gehlenite and gehlenite - sodium gehlenite.