Changes

Textures of sandstones can be qualitatively described by using standard images to estimate the [[Grain size|size]], [[Core_description#Maturity|sorting]], sphericity, and roundness of clastic particles. Quantitative textural analysis involves measurement of a certain number of grains (commonly 100 per thin section) so that mean grain size and sorting (standard deviation) can be calculated. Grain size measurements can be performed on a [http://www.gonda.ucla.edu/bri_core/trlight.htm transmitted light microscope] equipped with a graduated ocular lens, or they can be done by placing thin sections in a microfiche reader and measuring grains with a ruler. Whichever instrument is used, a glass slide inscribed with a metric scale must be used to determine a conversion factor for converting raw data to millimeters.

Textures of sandstones can be qualitatively described by using standard images to estimate the [[Grain size|size]], [[Core_description#Maturity|sorting]], sphericity, and roundness of clastic particles. Quantitative textural analysis involves measurement of a certain number of grains (commonly 100 per thin section) so that mean grain size and sorting (standard deviation) can be calculated. Grain size measurements can be performed on a [http://www.gonda.ucla.edu/bri_core/trlight.htm transmitted light microscope] equipped with a graduated ocular lens, or they can be done by placing thin sections in a microfiche reader and measuring grains with a ruler. Whichever instrument is used, a glass slide inscribed with a metric scale must be used to determine a conversion factor for converting raw data to millimeters.

Once data are converted to millimeters, it is also recommended that the data be converted to the phi scale, where the grain size in phi = –log₂ × grain size in mm. Mean grain size and sorting (standard deviation of grain size measurements) are then calculated. Mean grain size can be expressed in either the millimeter or phi scale, but sorting must be expressed in the phi scale to maintain a sorting index that is useful across a wide range of grain sizes.

Once data are converted to millimeters, it is also recommended that the data be converted to the [[phi scale]], where the grain size in phi = –log₂ × grain size in mm. Mean grain size and sorting (standard deviation of grain size measurements) are then calculated. Mean grain size can be expressed in either the millimeter or phi scale, but sorting must be expressed in the phi scale to maintain a sorting index that is useful across a wide range of grain sizes.

==Sandstone reservoirs==

==Sandstone reservoirs==