Light micrograph of a section of human lung tissue showing silicosis of the lung. Silicosis is a type of pneumoconiosis disease of the lungs caused by excessive or chronic exposure to silica dust. It is a long term lung disease caused by inhaling large amounts of crystalline silica dust, usually over many years. Silica is a substance naturally found in certain types of stone, rock, sands and clay. Working with these materials can create a very fine dust that can be easily inhaled.