Green Aventurine Quartz is actually a rock, not a mineral, composed essentially of interlocking macrocrystalline quartz grains with disseminated grains of other color imparting minerals. When a quartz-rich sedimentary deposit or a sandstone undergoes high grade metamorphism (metamorphism is the alteration of a rock due to changes in heat, pressure or chemical environment), the original material alters to a compact rock composed of interlocking quartz grains known as quartzite. If chromium is present then the green colored muscovite mica variety fuchsite can occur disseminated throughout the quartzite in parallel orientation giving it a green color and a spangled effect. This material is known as green aventurine quartz.
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