Complex sentence: A breccia pipe, also referred to as a chimney, is a mass of breccia, often in an irregular and cylindrical shape, that appears as an iron-stained knob, from several feet to several hundred feet in diameter.
Split into simpler sentences: A breccia pipe, also referred to as a chimney, is a mass of breccia, often in an irregular and cylindrical shape. When exposed at the surface, a breccia pipe may appear as an iron-stained knob, from several feet to several hundred feet in diameter.