A mass of fine grained and/or fractured rock, enclosing the main water bearing features.
The matrix has a lower permeability than the main water yielding horizon or fracture, but consists of the biggest mass of rock and therefore stores the biggest volume of groundwater.
Why is the matrix important?
The matrix in an aquifer stores the largest amount of groundwater. Water is transferred from the matrix to the fracture or high permeability zone when abstraction takes place.