This is a characteristic of a dry solid material to compress and/or harden, usually due to head-load or another type of pressure. Generally, pressure sensitive or cohesive materials will compact. Also, very fine (very small particle size) materials often exhibit this characteristic.
to draw together or compress (to pack or make hard) Consistency (Consistencies)-- the degree of thickness, firmness, or stickiness Crushed-- to squeeze together so as to break or destroy the natural shape or condition Crystal-- something transparent (clear) like crystal