remains than can fit into the lattice structure of the alkali feldspar that replaces the plagioclase. The result is ghost myrmekite – either as tiny quartz ovoids in remnant albite islands in the alkali feldspar or as tiny quartz ovoids as clusters without albite hosts in the alkali feldspar (see illustration). Examples for this structure are found in California in the Mount Rubidoux leucogranite and in granodiorites in the Sierra Nevada. Myrmekite formed during Ca-metasomatism During Ca- metasomatism myrmekite can be formed under different circumstances: Ca-metasomatism of deformed K-feldspar in magmatic rocks Ca-metasomatism of deformed K-feldspar in charnockites Ca-metasomatism of deformed plagioclase in anorthosites Ca-metasomatism of deformed K-feldspar in magmatic rocks Here Ca-bearing fluids enter primary alkali feldspar through cracks and react with the alkali feldspar. Through this reaction cracks are filled with quartz and myrmekite. The replacement reactions can affect large portions (> 60%) of the primary alkali feldspar. An important distinctive feature of this type of myrmekite formation is the constant thickness of the vermicules, whereas in the K-metasomatism their thickness changes as a function of the Ca-content of the plagioclase and they also taper towards the alkali feldspar. An example for this type of Ca-metasomatism is found in a megacrystal granite near Alastaro in Finland. Ca-metasomatism of deformed K-feldspar in charnockites The process stays the same, the only difference being the country rocks the Ca-bearing fluids act upon. Charnockites distinguish themselves from ordinary granitoids by the appearance of orthopyroxene (hypersthene) and can also be of metamorphic origin. An example for this type of Ca-metasomatism is found in Sri Lanka. Ca-metasomatism of deformed plagioclase in anorthosites In this type of Ca-metasomatism instead of the alkali feldspar it is the ubiquitous plagioclase that gets attacked by the Ca-bearing fluids. The resulting myrmekite also shows vermicules with constant thickness but unlike in the first case the vermicules formed in anorthosites can taper locally to the primary, non-quartz-bearing plagioclase. This behaviour can be explained by the incorporation of Na demanding more silica in the feldspar lattice. Examples are found in layered igneous complexes. Myrmekite formed during Na-Ca-metasomatism A first variety of this type of metasomatism affects only enclaves within a granitoid. Here the influx of Na-rich fluids in the temperature range 450 °C to 650 °C from the host leads to the replacement of alkali feldspar by myrmekite within the enclaves. During this process a reequilibration with the Na-poorer feldspars (plagioclase)