ERSC 2P16 Lecture 13: The Classification of Clastic Sedimentary Rocks Part 2
3 Aug 2015
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I) textural maturity: changes in grain size and shape. The name of a sandstone tells you something of its maturity. E. g. , a quartz arenite has less than 15% matrix and is better sorted than a quartz graywacke. The quartz arenite is more mature (greater transport distance and/or more times through the rock cycle) than the quartz graywacke: compositional maturity: compositional maturity is reflected by the relative proportion of physically soft or chemically unstable grains. The fewer the soft or unstable grains, the more mature the sediment. Bowen"s reaction series shows the sequence in which minerals crystallize from a cooling magma. Mineral stability can also be shown using bowen"s reaction series: the earliest minerals to crystallize are the least stable. Quartz is the most stable of the common mineral; it resists chemcial weathering and is the most common mineral in most sedimentary rocks. Potassium feldspar is also common but muscovite is relatively soft and breaks down during transport.
