An example for the formation of wartlike myrmekite can be found at the Palm quartz monzonite which issued from an older, yet undated diorite. Examples for this structure are found in California in the Rubidoux Mountain leucogranite and in granodiorites in the Sierra Nevada. Ca-metasomatism of deformed K-feldspar in magmatic rocks 250px| Fractured alkali feldspar filled with central quartz and myrmekite during Ca-metasomatism 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. Myrmekite formed during Na-Ca-metasomatism 250px| Myrmekite replacing K-feldspar in perthite during Na-Ca-metasomatism, showing isolated quartz vermicules of irregular shape. Lyon Mountain granite gneiss, Ausable Forks, New York 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) in the enclaves takes place. As a consequence Ca gets released in plagioclase which in turn can now react upon K-feldspar to form myrmekite. Basically this process is very similar to the Ca-metasomatism on K-feldspar described above except for the Na-fluids acting as a trigger.
An example for the formation of wartlike myrmekite can be found at the Twentynine Palms, California quartz monzonite which issued from an older, yet undated diorite. Examples for this structure are found in California in the Mount Rubidoux leucogranite and in granodiorites in the Sierra Nevada. Ca-metasomatism of deformed K-feldspar in magmatic rocks Fractured alkali feldspar filled with central quartz and myrmekite during Ca-metasomatism 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. Myrmekite formed during Na-Ca-metasomatism Myrmekite replacing K-feldspar in perthite during Na-Ca-metasomatism, showing isolated quartz vermicules of irregular shape. Lyon Mountain granite gneiss, Ausable Forks, New York 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) in the enclaves takes place. As a consequence Ca gets released in plagioclase which in turn can now react upon K-feldspar to form myrmekite. Basically this process is very similar to the Ca-metasomatism on K-feldspar described above except for the Na-fluids acting as a trigger.
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Palm
Twentynine Palms, California
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Rubidoux Mountain
Mount Rubidoux
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