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==Petrographic examples==

==Petrographic examples==

[[file:M109CH01Polycrystalline.jpg|400px|Triassic Sherwood Sandstone Group, County Antrim, Northern Ireland, U.K., polycrystalline quartz grain of metamorphic origin. The grain has sutured internal boundaries between composite crystals and a preferential alignment of the constituent crystals. In addition, crystal boundaries are diffuse. XPL, AFeS, KFS, BDI, Scale bar = 0.07 mm.]]

[[file:M109CH01Polychristalline.jpg|center|400px|thumb|Triassic Sherwood Sandstone Group, County Antrim, Northern Ireland, U.K., polycrystalline quartz grain of metamorphic origin. The grain has sutured internal boundaries between composite crystals and a preferential alignment of the constituent crystals. In addition, crystal boundaries are diffuse. XPL, AFeS, KFS, BDI, Scale bar = 0.07 mm.]]

 

[[file:M109CH01Monocrystalline.jpg|center|400px|thumb|Lower Cretaceous Travis Peak Formation, Eastland County, Texas, monocrystalline quartz grain with exceptionally abundant vacuoles (probably liquid-filled inclusions) and semicomposite extinction (Krynine’s “hydrothermal” quartz). Such vacuole-rich quartz grains are most commonly derived from hydrothermal-vein sources. The quartz overgrowth (cement) around the upper part of the grain has far fewer inclusions. XPL, Scale bar = 0.26 mm.]]

==See also==

==See also==