Experimental Studies on K-Rich Rocks - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 383

Fig. 13.3 a and b phase relations on two samples of a 79 AD Vesuvian lava flow. Px:
cllinopyroxene, San: sanidine, Pl: Plagoclase, Amph: amphibole, Lc: leucite (after Shea et al. 2009)

6KMg 3 AlSi 3 O 10 (OH) 2 + 4CaMgSi 2 O 6 10Mg 2 SiO 4 +2Ca 2 MgSi 2 O 7 +6KAlSi 2 O 6 +6H 2 O

ð Þ ð Þ ð Þ ð Þ ð Þ

phlogopite diopside forsterite akermanite leucite

This experimental study suggests that an assemblage consisting of forsterite,
akermanite, and leucite should be stable only at high temperatures and low P (H 2 O),
but would be converted to a phlogopite and pyroxene-bearing assemblage at high
water pressures. The above study, suggests that katungites were formed under
volcanic to subvolcanic conditions, and they are represented at greater depths by
phlogopite pyroxenite, closest equivalent of which is a madupite.