The formation of these structures can be modeled by the Tillotson equation of state, though more recently the semi-analytical ANEOS model is often used instead. Oblique examples of these structures are often associated with a characteristic “butterfly” pattern of rock deposits. Gault et al. divided the formation of these structures into three stages, during which shock and rarefaction waves compress the surrounding material. The (15[1])true depth of these structures is measured to the bottom of the (*) breccia (“BREH-chah”) lens, which covers the base of the simple (-5[1])type of these structures. The discovery of coesite and stishovite near one of these structures, which can have peak ring and multi-ring variants, (10[1])led to a theory of their formation developed by Eugene Shoemaker. (10[1])For 10 points, shocked quartz (10[1])and high (10[1])levels of iridium are often found (10[2])near what structures, (10[1])a prominent example of which is located near Chicxulub ■END■ (10[1])