WHY is chemical cement less abundant in SHALE? WHY is it variable in conglomerate?
Chemical cement in shale is less abundant because shale particles are so small can normally bind the rock together without an additional bonding from a chemical cement. Chemical cement in sandstone (NOT part of your question), is much more abundant because the particle size - normally visible quartz grains - is such that the rock would disintegrate, as unconsolidated sand, if it were not present. Chemical cement in conglomerate is variable because conglomerate is variable. Is the conglomerate pebble supported or matrix supported? A pebble supported conglomerate may be bound together with a later chemical cement. A matrix supported conglomerate may be bound by the sand or clay rich matrix which will not require any later infilling cement.
