I collected this in 1973 near Flagstaff in the San Francisco Peaks region while directing field camp for the University of Arizona. What I like best about it is its internal galaxy of rotation, giving a sense for how it spun during flight. Furthermore, I'm impressed with the thousands of vesicles representing escaping of gas.
Basaltic eruptions normally include the ejection of globs of magma, that initially are dough-like (i.e., viscous) and full of escaping gas. I picture the globs as pizza dough. During their brief flight, the globs can wrap themselves into spindle shaped masses, called 'bombs,' and achieve best aerodynamics.
Age & Formation
Less than 1 million years.